TerminatedNCT03519178Updated Nov 14, 2025Results posted

A Study of PF-06873600 in People With Cancer

A Phase 1/2 interventional study of PF-06873600 and Endocrine Therapy 1 in HR+ HER2- Metastatic Breast Cancer, Ovarian Cancer, Fallopian Tube Cancer, Primary Peritoneal Cancer, Triple Negative Breast Cancer, Male Breast Cancer, sponsored by Pfizer. Terminated at 54 sites in 6 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2025-11-14.

Sponsored by Pfizer · Phase 1/2, Interventional, and Treatment

Why this study was terminated

Per business decision, but not due to safety concerns or regulatory request.

Phase: Phase 1/2
Study type: Interventional
Enrollment: 155
Allocation: Non-randomized
Ages: 18 Years and older
Sex: All

Study summary

The purpose of this clinical trial is to learn about the safety and effects of study medicine (PF-06873600) when taken alone or with hormone therapy by people with cancer.

People may be able to participate in this study if they have the following types of cancer: Hormone Receptor positive (HR+) breast cancer; Human Epidermal Growth Factor Receptor 2 (HER2)-negative breast cancer that is advanced or metastatic (spread to other parts of the body); triple negative breast cancer; epithelial ovarian cancer; fallopian tube cancer; or primary peritoneal cancer.

All participants in this study will receive the study medicine by mouth, 1 to 2 times a day at home. The dose of the study medicine may be changed during the study.

Some participants will also receive hormone therapy. The hormone therapy will be either letrozole by mouth once a day at home, or fulvestrant as a shot into the muscle. Fulvestrant will be given every two weeks at the study clinic for the first month, and then once a month after that.

Participants will take part in this study for at least 7 to 8 months, depending on how they respond to the therapy. During this time participants will visit the study clinic once a week for the first 2 cycles and every cycle thereafter.

Read the detailed description

This is a Phase 1/2a, open-label, multi-center, non-randomized, multiple dose, safety, tolerability, pharmacokinetic, and pharmacodynamic study of PF-06873600 administered as a single agent in sequential dose levels and then in combination with endocrine therapy. In Part 1A and Part 1C, successive cohorts of patients will receive escalating doses of PF-06873600 and then in dose finding (Part 1B) with PF-06873600 in combination with endocrine therapy (ET). This study contains 2 parts, dose escalation with single agent (Part 1A and 1C) and then dose finding with PF-06873600 in combination with endocrine therapy (Part 1B) followed by dose expansion arms of PF-06873600 in combination with endocrine therapy (Part 2).

Conditions studied

HR+ HER2- Metastatic Breast Cancer, Ovarian Cancer, Fallopian Tube Cancer, Primary Peritoneal Cancer, Triple Negative Breast Cancer, Male Breast Cancer

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Keywords

Hormone Receptor (HR) Positive Breast Cancer
Estrogen receptor (ER) positive
Progesterone receptor (PR) positive
Cyclin-dependent kinase (CDK)
Human epidermal growth factor receptor 2 (HER2) negative
Advanced breast cancer
Metastatic breast cancer (MBC)
Triple negative breast cancer (TNBC)
Epithelial ovarian cancer (EOC)
Fallopian tube cancer
Primary peritoneal cancer (PPC)
CDK4/6 inhibitor
Endocrine Therapy (ET)
Measurable disease
Luteinizing Hormone Releasing Hormone (LHRH) Agonist
Goserelin
Leuprolide acetate

In context

Ovarian Neoplasms

2,695 studies on the registry are indexed under Ovarian Neoplasms; 727 are open to participants now.

This study's enrollment of 155 is above the median of 60 across 2,030 interventional studies indexed under Ovarian Neoplasms.

Browse Ovarian Neoplasms studies →

Lead sponsor

Pfizer is the lead sponsor of 3,244 studies on the registry; 139 are open to participants now.

Of its 582 completed or terminated interventional studies of FDA-regulated products, 381 (65%) have results posted.

Counted across the registry records on this site, refreshed daily.

Who can participate

Ages eligible: 18 Years and older
Sexes eligible: All
Accepts healthy volunteers: No

Inclusion criteria

Have a diagnosis of Hormone Receptor Positive (HR+), Human Epidermal Growth Factor Receptor 2 Negative (HER2-) breast cancer
- Prior combined CDK 4/6 inhibitor and endocrine therapy and 1 or 2 prior lines of chemotherapy
Have a diagnosis of metastatic triple negative breast cancer (TNBC)
- Up to 1-2 prior lines of chemotherapy
Have a diagnosis of advanced platinum resistant epithelial ovarian cancer (EOC)/fallopian tube cancer/primary peritoneal cancer (PPC)
- Up to 2-3 prior lines of therapy
Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0 or 1
Measurable disease or non-measurable disease and refractory to or intolerant of existing therapies (Part 1)
Measurable disease as defined by RECIST 1.1 is required (Part 1B and Part 2 only)

Exclusion criteria

Exclusion Criteria:

Known active uncontrolled or symptomatic Central Nervous System (CNS) metastases
Other active malignancy within 3 years prior to randomization, except for adequately treated basal cell or squamous cell skin cancer, or carcinoma in situ
Major surgery or radiation within 4 weeks prior to study entry
Last anti-cancer treatment within 2 weeks prior to study entry
Participation in other studies involving investigational drug(s) within 4 weeks prior to study entry
Pregnant or breastfeeding female patients
Active inflammatory gastrointestinal (GI) disease, known diverticular disease or previous gastric resection or lap band surgery including impairment of gastro intestinal function or GI disease

Study design

Phase: Phase 1 / Phase 2
Primary purpose: Treatment
Allocation: Non-randomized
Intervention model: Sequential assignment
Masking: None (open label)
Enrollment: 155 participants (actual)

Study arms

Experimental
Dose Escalation
Single Agent Dose Escalation
Drug: PF-06873600
Experimental
Dose Finding Endocrine Therapy 1 Combination
Part 1B PF-06873600 plus Endocrine Therapy 1
Drug: PF-06873600 · Drug: Endocrine Therapy 1
Experimental
Dose Finding Endocrine Therapy 2 Combination
Part 1B PF-06873600 plus Endocrine Therapy 2
Drug: PF-06873600 · Drug: Endocrine Therapy 2
Experimental
Dose Expansion Arm A
PF-06873600 as a Single Agent
Drug: PF-06873600
Experimental
Dose Expansion Arm B
PF-06873600 as a Single Agent in Various Tumor Types
Drug: PF-06873600
Experimental
Dose Expansion Arm C
PF-06873600 in Combination with Endocrine Therapy 1
Drug: PF-06873600 · Drug: Endocrine Therapy 1
Experimental
Dose Expansion Arm D
PF-06873600 in Combination with Endocrine Therapy 1
Drug: PF-06873600 · Drug: Endocrine Therapy 1
Experimental
Dose Expansion Arm E
PF-06873600 in Combination with Endocrine Therapy 2
Drug: PF-06873600 · Drug: Endocrine Therapy 2

Interventions

DrugPF-06873600
PF-06873600 tablet for oral dosing
DrugEndocrine Therapy 1
Endocrine Therapy 1
DrugEndocrine Therapy 2
Endocrine Therapy 2

What researchers measure

Primary outcomes

Number of Participants With Dose Limiting Toxicities (DLTs) - Part 1
DLT was defined as any of the following adverse events (AEs) occurring in the first cycle of treatment (28 days) which were attributable to one, the other, or both agents in the combination: Hematologic - grade(G) 4 neutropenia lasting \>7 days; Febrile neutropenia defined as an absolute neutrophil count (ANC) \<1.0 \* 10\^9/L with a single temperature of \>38.3°C, or a sustained temperature of ≥38°C, for more than 1 hour; G≥3 neutropenia with associated infection; G3 thrombocytopenia with clinically significant bleeding as indicated by ≥ G2 bleeding; G4 thrombocytopenia. Nonhematologic: Confirmed case of Drug Induced Liver Injury (DILI) (Hy's Law); G≥3 AEs that were clinically significant.
Time frame: Cycle 1 (within 28 days after the first dose of study intervention)
Number of Participants With Adverse Events (AEs) and Serious AEs (SAEs) - Part 1 + Part 2
An AE was defined as the appearance of (or worsening of any pre-existing) undesirable sign(s), symptom(s), or medical condition(s) that occurred after participants' signed informed consent has been obtained. An SAE was an AE resulting in any of the following outcomes: was fatal or life-threatening; resulted in persistent or significant disability/incapacity; constituted a congenital anomaly/birth defect; was medically significant; required inpatient hospitalization or prolongation of existing hospitalization. Treatment Related AEs were treatment emergent AEs with cause categorized by the investigator as related to study treatment.
Time frame: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Number of Participants With Worst Post-Baseline Hematology Results Based on Common Terminology Criteria for Adverse Events (CTCAE) Grade: Part 1 + Part 2
Severity was graded as NCI CTCAE version 4.03:Grade 1: asymptomatic or mild symptoms, clinical or diagnostic observations only, intervention not indicated; Grade 2: moderate, minimal, local or noninvasive intervention indicated, limiting age-appropriate instrumental activities of daily life (ADL); Grade 3: severe or medically significant but not immediately life-threatening, hospitalization or prolongation of existing hospitalization indicated, disabling, limiting self-care ADL; Grade 4: life-threatening consequence, urgent intervention indicated; Grade 5: death related to AE.
Time frame: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Number of Participants With Worst Post-Baseline Chemistry Results Based on Common Terminology Criteria for Adverse Events (CTCAE) Grade: Part 1 + Part 2
Severity was graded as NCI CTCAE version 4.03:Grade 1: asymptomatic or mild symptoms, clinical or diagnostic observations only, intervention not indicated; Grade 2: moderate, minimal, local or noninvasive intervention indicated, limiting age-appropriate instrumental activities of daily life (ADL); Grade 3: severe or medically significant but not immediately life-threatening, hospitalization or prolongation of existing hospitalization indicated, disabling, limiting self-care ADL; Grade 4: life-threatening consequence, urgent intervention indicated; Grade 5: death related to AE.
Time frame: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Number of Participants With Post-Baseline Vital Sign Abnormalities Meeting Pre-Defined Categorization - Part 1 + Part 2
Pre-defined criteria included: 1) systolic blood pressure (SBP) (mm Hg) minimum (min) value \<90; 2) SBP change from baseline (CFB) (mm Hg) maximum (max) decrease \>=30 or max increase \>=30; 3) diastolic blood pressure (DBP) (mm Hg) min \<50; 4) DBP CFB (mm Hg) max decrease \>=20 or max increase \>=20; 5) supine heart rate (HR) beats per minute (bpm) min \<40 or max \>120.
Time frame: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Number of Participants With Post-Baseline Electrocardiogram (ECG) Changes Meeting Pre-Defined Categorization - Part 1 + Part 2
ECG pre-defined categories for QTc interval adjusted according to Fridericia formula (QTcF) (msec) included: 450 \<= max. \<=480, 481 \<= max. \<=500, max \>=501; QTcF CFB: 30 \< max \<=60, max \>60; for PR and QRS: PR (msec): max \>=300; PR increase from baseline: Baseline \>200 and max. \>=25% increase, Baseline \<=200 and max. \>=50% increase; QRS (msec): max \>=200; QRS (msec) increase from baseline: Baseline \>100 and max. \>=25% increase, Baseline \<=100 and max. \>=50% increase. Categories, with at least 1 participant having ECG abnormality in any of the reporting arms, were reported in this outcome measure.
Time frame: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Overall Response Rate (ORR): Part 2
ORR: percentage of participants with confirmed complete response (CR) or partial response (PR). Response evaluation criteria in solid tumors (RECIST) v1.1: a) CR = disappearance of all non-nodal target lesions. In addition, any pathological lymph nodes assigned as target lesions that had a reduction in short axis to less than (\<) 10 millimeter (mm). Disappearance of all non-target lesions. In addition, all lymph nodes assigned a non-target lesion must be non-pathological in size (\<10 mm short axis) and b) PR = at least a 30 percent (%) decrease in the sum of diameter of all target lesions, taking as reference the baseline sum of diameters. Any radiological assessments taken more than 30 days after the last dose of study therapy or after antineoplastic agents other than study treatments taken by the participants was excluded from the best overall response derivation. Confirmation of CR or PR was to be at least 4 weeks apart from the previous radiological assessment.
Time frame: From the start of the treatment until disease/clinical progression or death or early study discontinuation, whichever happened earlier (approximately up to 24 months)

Secondary outcomes

Maximum Observed Plasma Concentration (Cmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2
The maximum observed concentration of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. The Cmax value was observed directly from data.
Time frame: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on Cycle 1 Day 1 (C1D1); Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D1
Time to Reach Cmax at Steady State (Tmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2
Tmax of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported.
Time frame: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D1
Area Under the Concentration-Time Profile From Time 0 to the Time of the Last Quantifiable Concentration (AUClast) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
AUClast of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Area Under the Concentration-Time Profile From Time 0 Extrapolated to Infinite Time (AUCinf) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
AUCinf of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Apparent Clearance (CL/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
CL/F of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Apparent Volume of Distribution (Vz/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
Vz/F of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Terminal Half-life (t1/2) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
t1/2 of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Steady State Maximum Concentration (Css,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2
Css,max of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Time to Maximum Plasma Concentration at Steady State (Tss,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2
Tss,max of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Steady State Minimum Plasma Concentration (Css,Min) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2
Css,min of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Steady-State Area Under the Plasma Concentration Versus Time Curve Within One Dose Interval (AUCss,Tau) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
AUCss,tau of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Steady-State Apparent Oral Plasma Clearance (CLss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
CLss/F of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Apparent Volume of Distribution at Steady State (Vss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
Vss/F of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Accumulation Ratio Based on AUC (Rac) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
Rac of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").
Time frame: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Accumulation Ratio Based on Cmax (Observed) (Rac,Cmax) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 2
Rac,cmax of PF-06873600 after multiple doses of study intervention when given as in combination with fulvestrant (Part 2) was reported.
Time frame: Pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Pharmacodynamic (PD) Biomarker Phospho-retinoblastoma Protein (pRb) in Tumor Tissue in Participants - Part 1 + Part 2
Level of the PD marker, pRb, was analyzed at 2 time points, at screening and at Cycle 2 Day 1. Percentage changes of pRb at Cycle 2 Day 1 from screening (baseline) were calculated.
Time frame: Screening and Cycle 2 Day 1
PD Biomarker Ki67 in Tumor Tissue in Participants - Part 1 + Part 2
Level of the PD marker, Ki67, was analyzed at 2 time points, at screening and at Cycle 2 Day 1. Percent changes of pRb at Cycle 2 Day 1 from screening (baseline) were calculated.
Time frame: Screening and Cycle 2 Day 1

Results

Posted Jul 31, 2024

Participant flow

Participants with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced or metastatic breast cancer (mBC), with locally recurrent/advanced or metastatic triple negative breast cancer (TNBC) or advanced platinum resistant ovarian/fallopian/peritoneal cancer, were recruited into this study. Two participants assigned to treatment but did not receive any study treatment were not included in any analysis.

PF-06873600 Treatment

Participant flow — PF-06873600 Treatment
Milestone	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Started	1	2	2	3	9	7	4	13	10	9	7	5	6	45	28
Completed	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Not completed	1	2	2	3	9	7	4	13	10	9	7	5	6	45	28
Withdrew: Adverse event	0	0	0	0	0	0	0	2	1	0	0	0	1	3	2
Withdrew: Death	0	0	0	0	0	0	0	0	1	1	0	0	0	0	1
Withdrew: Physician decision	0	0	0	0	0	0	0	1	0	0	1	0	0	4	1
Withdrew: Progressive disease	1	1	1	1	6	7	3	7	3	5	4	3	4	28	8
Withdrew: Withdrawal by subject	0	0	1	0	2	0	0	1	3	2	0	2	1	1	2
Withdrew: Global deterioration of health status	0	0	0	2	0	0	1	2	1	1	2	0	0	3	0
Withdrew: Refused further treatment	0	1	0	0	1	0	0	0	0	0	0	0	0	0	1
Withdrew: Other	0	0	0	0	0	0	0	0	1	0	0	0	0	1	3
Withdrew: Lost to follow-up	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1
Withdrew: Study terminated by sponsor	0	0	0	0	0	0	0	0	0	0	0	0	0	5	9

Fulvestrant. Treatment

Participant flow — Fulvestrant. Treatment
Milestone	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Started	9	45	28
Completed	0	0	0
Not completed	9	45	28
Withdrew: Adverse event	0	1	0
Withdrew: Death	1	0	1
Withdrew: Lost to follow-up	0	0	1
Withdrew: Physician decision	0	4	2
Withdrew: Progressive disease	5	30	8
Withdrew: Study terminated by sponsor	0	5	9
Withdrew: Withdrawal by subject	2	1	2
Withdrew: Global deterioration of health status	1	3	0
Withdrew: Refused further treatment	0	0	2
Withdrew: Other	0	1	3

Letrozole Treatment

Participant flow — Letrozole Treatment
Milestone	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Started	0	0	0	0	0	0	0	0	0	0	7	0	0	0	0
Completed	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Not completed	0	0	0	0	0	0	0	0	0	0	7	0	0	0	0
Withdrew: Physician decision	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0
Withdrew: Progressive disease	0	0	0	0	0	0	0	0	0	0	4	0	0	0	0
Withdrew: Global deterioration of health status	0	0	0	0	0	0	0	0	0	0	2	0	0	0	0

Follow-Up

Participant flow — Follow-Up
Milestone	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Started	1	2	2	3	9	7	4	13	10	9	7	5	6
Completed	0	0	0	0	4	3	1	2	1	6	4	0	2
Not completed	1	2	2	3	5	4	3	11	9	3	3	5	4
Withdrew: Death	0	0	0	0	0	0	0	0	3	1	0	0	2
Withdrew: Lost to follow-up	0	0	0	0	0	3	1	4	1	0	0	0	0
Withdrew: Withdrawal by subject	1	2	2	3	5	1	2	6	5	2	3	5	2
Withdrew: Other	0	0	0	0	0	0	0	1	0	0	0	0	0

Long-term Follow-up

Participant flow — Long-term Follow-up
Milestone	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Started	45	28
Completed	0	0
Not completed	45	28
Withdrew: Death	4	4
Withdrew: Lost to follow-up	1	1
Withdrew: Study terminated by sponsor	32	19
Withdrew: Withdrawal by subject	7	3
Withdrew: Other	0	1
Withdrew: Global deterioration of health status	1	0

Outcome measures

PrimaryNumber of Participants With Dose Limiting Toxicities (DLTs) - Part 1

DLT was defined as any of the following adverse events (AEs) occurring in the first cycle of treatment (28 days) which were attributable to one, the other, or both agents in the combination: Hematologic - grade(G) 4 neutropenia lasting \>7 days; Febrile neutropenia defined as an absolute neutrophil count (ANC) \<1.0 \* 10\^9/L with a single temperature of \>38.3°C, or a sustained temperature of ≥38°C, for more than 1 hour; G≥3 neutropenia with associated infection; G3 thrombocytopenia with clinically significant bleeding as indicated by ≥ G2 bleeding; G4 thrombocytopenia. Nonhematologic: Confirmed case of Drug Induced Liver Injury (DILI) (Hy's Law); G≥3 AEs that were clinically significant.

Time frame:: Cycle 1 (within 28 days after the first dose of study intervention)
Reported as:: Count of participants · Participants

Number of Participants With Dose Limiting Toxicities (DLTs) - Part 1
Participants	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Number of Participants With Dose Limiting Toxicities (DLTs) - Part 1	0	0	0	0	0	0	2	0	4	0	0	0	0

PrimaryNumber of Participants With Adverse Events (AEs) and Serious AEs (SAEs) - Part 1 + Part 2

An AE was defined as the appearance of (or worsening of any pre-existing) undesirable sign(s), symptom(s), or medical condition(s) that occurred after participants' signed informed consent has been obtained. An SAE was an AE resulting in any of the following outcomes: was fatal or life-threatening; resulted in persistent or significant disability/incapacity; constituted a congenital anomaly/birth defect; was medically significant; required inpatient hospitalization or prolongation of existing hospitalization. Treatment Related AEs were treatment emergent AEs with cause categorized by the investigator as related to study treatment.

Time frame:: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Reported as:: Count of participants · Participants

Number of Participants With Adverse Events (AEs) and Serious AEs (SAEs) - Part 1 + Part 2
Participants	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
All-causality AEs	1	2	2	3	9	6	4	13	10	9	7	5	6	45	25
All-causality SAEs	0	1	0	0	2	0	1	4	6	1	2	0	3	9	5
Treatment-related AEs	0	2	1	0	8	6	4	13	10	8	7	5	5	45	24
Treatment-related SAEs	0	0	0	0	0	0	0	0	3	1	1	0	1	5	2

PrimaryNumber of Participants With Worst Post-Baseline Hematology Results Based on Common Terminology Criteria for Adverse Events (CTCAE) Grade: Part 1 + Part 2

Severity was graded as NCI CTCAE version 4.03:Grade 1: asymptomatic or mild symptoms, clinical or diagnostic observations only, intervention not indicated; Grade 2: moderate, minimal, local or noninvasive intervention indicated, limiting age-appropriate instrumental activities of daily life (ADL); Grade 3: severe or medically significant but not immediately life-threatening, hospitalization or prolongation of existing hospitalization indicated, disabling, limiting self-care ADL; Grade 4: life-threatening consequence, urgent intervention indicated; Grade 5: death related to AE.

Time frame:: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Reported as:: Count of participants · Participants

Number of Participants With Worst Post-Baseline Hematology Results Based on Common Terminology Criteria for Adverse Events (CTCAE) Grade: Part 1 + Part 2
Participants	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Activated partial thromboplastin time prolonged — Grade 0	1	2	2	2	7	7	3	5	6	7	5	4	6	33	13
Activated partial thromboplastin time prolonged — Grade 1	0	0	0	0	1	0	1	3	0	1	0	0	0	3	1
Activated partial thromboplastin time prolonged — Grade 2	0	0	0	0	0	0	0	0	0	0	1	0	0	0	0
Activated partial thromboplastin time prolonged — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0
Activated partial thromboplastin time prolonged — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Anemia — Grade 0	0	0	1	0	0	2	0	1	1	0	1	0	1	9	5
Anemia — Grade 1	1	2	0	3	2	3	0	5	0	4	3	4	3	10	12
Anemia — Grade 2	0	0	1	0	5	2	2	6	5	5	1	1	0	19	5
Anemia — Grade 3	0	0	0	0	2	0	2	1	4	0	2	0	2	7	4
Anemia — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Hemoglobin increased — Grade 0	1	2	2	3	9	7	4	13	10	9	7	5	6	45	26
Hemoglobin increased — Grade 1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hemoglobin increased — Grade 2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hemoglobin increased — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hemoglobin increased — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
International normalized ratio (INR) increased — Grade 0	1	2	2	2	7	7	3	8	6	7	6	4	6	29	9
International normalized ratio (INR) increased — Grade 1	0	0	0	0	1	0	1	0	1	0	0	0	0	4	3
International normalized ratio (INR) increased — Grade 2	0	0	0	0	0	0	0	0	0	1	0	0	0	3	0
International normalized ratio (INR) increased — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
International normalized ratio (INR) increased — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Leukocytosis — Grade 0	1	2	2	3	9	7	4	13	10	9	7	5	6	45	26
Leukocytosis — Grade 1	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Leukocytosis — Grade 2	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Leukocytosis — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Leukocytosis — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Lymphocyte count decreased — Grade 0	1	2	2	2	3	2	1	3	2	3	2	2	1	14	15
Lymphocyte count decreased — Grade 1	0	0	0	0	0	0	0	2	1	2	0	2	0	6	4
Lymphocyte count decreased — Grade 2	0	0	0	1	4	3	2	6	1	1	4	0	4	21	5
Lymphocyte count decreased — Grade 3	0	0	0	0	2	2	0	2	6	3	1	1	1	4	2
Lymphocyte count decreased — Grade 4	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0
Lymphocyte count increased — Grade 0	1	2	2	3	9	7	4	13	10	9	7	5	6	45	26
Lymphocyte count increased — Grade 1	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Lymphocyte count increased — Grade 2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Lymphocyte count increased — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Lymphocyte count increased — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Neutrophil count decreased — Grade 0	1	1	2	3	4	5	0	6	4	7	2	2	0	16	8
Neutrophil count decreased — Grade 1	0	1	0	0	2	0	1	1	0	0	0	0	3	6	4
Neutrophil count decreased — Grade 2	0	0	0	0	2	2	0	4	2	0	5	3	1	7	9
Neutrophil count decreased — Grade 3	0	0	0	0	1	0	1	2	1	2	0	0	2	9	4
Neutrophil count decreased — Grade 4	0	0	0	0	0	0	2	0	3	0	0	0	0	7	1
Platelet count decreased — Grade 0	1	2	2	3	6	5	0	9	5	5	4	3	4	28	17
Platelet count decreased — Grade 1	0	0	0	0	1	2	2	3	3	3	3	2	2	14	8
Platelet count decreased — Grade 2	0	0	0	0	1	0	0	0	0	1	0	0	0	2	0
Platelet count decreased — Grade 3	0	0	0	0	1	0	1	1	0	0	0	0	0	1	1
Platelet count decreased — Grade 4	0	0	0	0	0	0	1	0	2	0	0	0	0	0	0
White blood cell decreased — Grade 0	1	1	2	1	4	2	0	0	3	2	0	2	0	11	7
White blood cell decreased — Grade 1	0	1	0	2	1	3	0	7	0	4	1	1	1	8	7
White blood cell decreased — Grade 2	0	0	0	0	4	2	1	5	3	3	6	2	4	16	8
White blood cell decreased — Grade 3	0	0	0	0	0	0	3	1	2	0	0	0	1	7	3
White blood cell decreased — Grade 4	0	0	0	0	0	0	0	0	2	0	0	0	0	3	1

PrimaryNumber of Participants With Worst Post-Baseline Chemistry Results Based on Common Terminology Criteria for Adverse Events (CTCAE) Grade: Part 1 + Part 2

Time frame:: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Reported as:: Count of participants · Participants

Number of Participants With Worst Post-Baseline Chemistry Results Based on Common Terminology Criteria for Adverse Events (CTCAE) Grade: Part 1 + Part 2
Participants	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Alanine aminotransferase increased — Grade 0	0	1	2	3	6	5	3	9	8	8	5	2	4	41	20
Alanine aminotransferase increased — Grade 1	0	1	0	0	3	2	1	3	1	1	1	2	2	4	3
Alanine aminotransferase increased — Grade 2	1	0	0	0	0	0	0	0	1	0	1	1	0	0	0
Alanine aminotransferase increased — Grade 3	0	0	0	0	0	0	0	1	0	0	0	0	0	0	1
Alanine aminotransferase increased — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Alkaline phosphatase increased — Grade 0	1	1	2	2	5	5	2	9	6	6	4	2	1	31	16
Alkaline phosphatase increased — Grade 1	0	1	0	1	2	1	2	2	4	3	3	2	4	13	6
Alkaline phosphatase increased — Grade 2	0	0	0	0	2	1	0	1	0	0	0	1	1	1	1
Alkaline phosphatase increased — Grade 3	0	0	0	0	0	0	0	1	0	0	0	0	0	0	1
Alkaline phosphatase increased — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Aspartate aminotransferase increased — Grade 0	0	1	2	2	5	6	2	9	7	6	3	2	2	38	16
Aspartate aminotransferase increased — Grade 1	0	1	0	1	2	1	2	3	3	2	4	3	3	5	6
Aspartate aminotransferase increased — Grade 2	1	0	0	0	2	0	0	0	0	1	0	0	1	2	1
Aspartate aminotransferase increased — Grade 3	0	0	0	0	0	0	0	1	0	0	0	0	0	0	1
Aspartate aminotransferase increased — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Blood bilirubin increased — Grade 0	1	2	2	3	9	7	4	13	8	9	7	5	6	45	19
Blood bilirubin increased — Grade 1	0	0	0	0	0	0	0	0	1	0	0	0	0	0	3
Blood bilirubin increased — Grade 2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1
Blood bilirubin increased — Grade 3	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0
Blood bilirubin increased — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1
Creatinine increased — Grade 0	0	0	0	1	5	3	1	3	3	5	2	0	1	21	7
Creatinine increased — Grade 1	1	2	2	2	4	4	3	8	5	4	5	5	5	22	17
Creatinine increased — Grade 2	0	0	0	0	0	0	0	2	2	0	0	0	0	2	0
Creatinine increased — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Creatinine increased — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypercalcemia — Grade 0	1	2	2	3	7	4	4	12	8	7	7	3	5	38	22
Hypercalcemia — Grade 1	0	0	0	0	2	3	0	1	2	1	0	2	1	5	2
Hypercalcemia — Grade 2	0	0	0	0	0	0	0	0	0	1	0	0	0	1	0
Hypercalcemia — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypercalcemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0
Hyperglycemia — Grade 0	1	2	2	2	6	5	4	10	6	6	5	5	4	23	12
Hyperglycemia — Grade 1	0	0	0	0	3	2	0	3	4	3	1	0	2	18	8
Hyperglycemia — Grade 2	0	0	0	1	0	0	0	0	0	0	0	0	0	2	3
Hyperglycemia — Grade 3	0	0	0	0	0	0	0	0	0	0	1	0	0	2	1
Hyperglycemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hyperkalemia — Grade 0	0	2	2	3	8	7	4	12	9	9	7	5	4	42	23
Hyperkalemia — Grade 1	1	0	0	0	1	0	0	1	0	0	0	0	1	1	1
Hyperkalemia — Grade 2	0	0	0	0	0	0	0	0	1	0	0	0	0	1	0
Hyperkalemia — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0
Hyperkalemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	1	0	0
Hypermagnesemia — Grade 0	1	2	1	3	9	7	4	12	7	9	6	5	6	42	15
Hypermagnesemia — Grade 1	0	0	1	0	0	0	0	1	3	0	1	0	0	3	8
Hypermagnesemia — Grade 2	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Hypermagnesemia — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1
Hypermagnesemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypernatremia — Grade 0	1	2	2	3	9	7	4	13	8	9	7	5	6	44	24
Hypernatremia — Grade 1	0	0	0	0	0	0	0	0	1	0	0	0	0	1	0
Hypernatremia — Grade 2	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypernatremia — Grade 3	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0
Hypernatremia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypoalbuminemia — Grade 0	1	2	2	2	4	4	3	11	5	8	6	5	5	35	18
Hypoalbuminemia — Grade 1	0	0	0	1	5	3	1	2	2	1	1	0	1	7	5
Hypoalbuminemia — Grade 2	0	0	0	0	0	0	0	0	2	0	0	0	0	3	1
Hypoalbuminemia — Grade 3	0	0	0	0	0	0	0	0	1	0	0	0	0	0	0
Hypoalbuminemia — Grade 4	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Hypocalcemia — Grade 0	1	2	2	3	8	7	4	10	7	7	4	5	6	36	13
Hypocalcemia — Grade 1	0	0	0	0	1	0	0	2	3	2	3	0	0	7	9
Hypocalcemia — Grade 2	0	0	0	0	0	0	0	0	0	0	0	0	0	1	2
Hypocalcemia — Grade 3	0	0	0	0	0	0	0	1	0	0	0	0	0	1	0
Hypocalcemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypoglycemia — Grade 0	1	2	2	3	8	7	3	13	10	8	7	5	6	44	23
Hypoglycemia — Grade 1	0	0	0	0	1	0	0	0	0	1	0	0	0	1	1
Hypoglycemia — Grade 2	0	0	0	0	0	0	1	0	0	0	0	0	0	0	0
Hypoglycemia — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypoglycemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypokalemia — Grade 0	1	2	2	2	8	6	3	10	7	8	6	5	5	33	19
Hypokalemia — Grade 1	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypokalemia — Grade 2	0	0	0	1	1	1	1	2	1	1	1	0	1	11	4
Hypokalemia — Grade 3	0	0	0	0	0	0	0	1	2	0	0	0	0	1	1
Hypokalemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypomagnesemia — Grade 0	1	2	2	1	5	4	3	7	8	3	2	5	4	24	14
Hypomagnesemia — Grade 1	0	0	0	2	4	2	1	5	2	6	5	0	2	20	10
Hypomagnesemia — Grade 2	0	0	0	0	0	1	0	1	0	0	0	0	0	0	0
Hypomagnesemia — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0
Hypomagnesemia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hyponatremia — Grade 0	1	1	0	1	5	3	3	12	3	8	5	4	3	40	20
Hyponatremia — Grade 1	0	1	2	2	4	4	1	1	7	1	2	1	3	5	3
Hyponatremia — Grade 2	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Hyponatremia — Grade 3	0	0	0	0	0	0	0	0	0	0	0	0	0	0	1
Hyponatremia — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Hypophosphatemia — Grade 0	1	2	2	3	7	5	3	9	8	7	6	5	6	39	22
Hypophosphatemia — Grade 1	0	0	0	0	0	0	0	0	0	0	0	0	0	1	2
Hypophosphatemia — Grade 2	0	0	0	0	1	2	1	3	1	2	1	0	0	3	0
Hypophosphatemia — Grade 3	0	0	0	0	1	0	0	1	0	0	0	0	0	1	0
Hypophosphatemia — Grade 4	0	0	0	0	0	0	0	0	1	0	0	0	0	1	0
Lipase increased — Grade 0	1	1	2	3	9	6	4	11	9	7	6	5	5	42	15
Lipase increased — Grade 1	0	0	0	0	0	0	0	1	1	0	1	0	1	2	5
Lipase increased — Grade 2	0	1	0	0	0	1	0	1	0	0	0	0	0	1	0
Lipase increased — Grade 3	0	0	0	0	0	0	0	0	0	1	0	0	0	0	4
Lipase increased — Grade 4	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0
Serum amylase increased — Grade 0	1	2	2	3	9	6	4	12	9	7	5	5	6	41	20
Serum amylase increased — Grade 1	0	0	0	0	0	1	0	1	1	1	2	0	0	3	4
Serum amylase increased — Grade 2	0	0	0	0	0	0	0	0	0	0	0	0	0	1	0
Serum amylase increased — Grade 3	0	0	0	0	0	0	0	0	0	1	0	0	0	0	0
Serum amylase increased — Grade 4	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0

PrimaryNumber of Participants With Post-Baseline Vital Sign Abnormalities Meeting Pre-Defined Categorization - Part 1 + Part 2

Pre-defined criteria included: 1) systolic blood pressure (SBP) (mm Hg) minimum (min) value \<90; 2) SBP change from baseline (CFB) (mm Hg) maximum (max) decrease \>=30 or max increase \>=30; 3) diastolic blood pressure (DBP) (mm Hg) min \<50; 4) DBP CFB (mm Hg) max decrease \>=20 or max increase \>=20; 5) supine heart rate (HR) beats per minute (bpm) min \<40 or max \>120.

Time frame:: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Reported as:: Count of participants · Participants

Number of Participants With Post-Baseline Vital Sign Abnormalities Meeting Pre-Defined Categorization - Part 1 + Part 2
Participants	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
SBP (mm Hg) <90	0	0	0	2	1	1	0	1	1	0	0	0	3	0
SBP CFB (mm Hg) >= 30 increase	0	0	0	1	1	0	3	2	0	0	1	0	5	2
SBP CFB (mm Hg) >= 30 decrease	0	1	1	0	0	0	1	3	3	1	1	0	13	2
DBP (mm Hg) <50	0	0	0	4	0	0	0	1	0	0	0	1	1	0
DBP CFB (mm Hg) >=20 increase	1	0	0	0	2	0	3	1	1	0	1	0	2	4
DBP CFB (mm Hg) >=20 decrease	0	0	0	3	1	0	0	3	0	2	1	0	10	4
Heart rate (bpm) <40	0	0	0	0	0	0	0	0	0	0	0	1	0	0
Heart rate (bpm) >120	0	0	0	2	0	0	0	2	1	0	0	0	1	0

PrimaryNumber of Participants With Post-Baseline Electrocardiogram (ECG) Changes Meeting Pre-Defined Categorization - Part 1 + Part 2

ECG pre-defined categories for QTc interval adjusted according to Fridericia formula (QTcF) (msec) included: 450 \<= max. \<=480, 481 \<= max. \<=500, max \>=501; QTcF CFB: 30 \< max \<=60, max \>60; for PR and QRS: PR (msec): max \>=300; PR increase from baseline: Baseline \>200 and max. \>=25% increase, Baseline \<=200 and max. \>=50% increase; QRS (msec): max \>=200; QRS (msec) increase from baseline: Baseline \>100 and max. \>=25% increase, Baseline \<=100 and max. \>=50% increase. Categories, with at least 1 participant having ECG abnormality in any of the reporting arms, were reported in this outcome measure.

Time frame:: Day 1 up to 28 days after the last dose of study intervention, up to approximately 24 months
Reported as:: Count of participants · Participants

Number of Participants With Post-Baseline Electrocardiogram (ECG) Changes Meeting Pre-Defined Categorization - Part 1 + Part 2
Participants	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
PR interval not otherwise specified (NOS) (msec) baseline >200 and percent change >=25%	0	0	0	0	0	0	0	0	0	0	0	1	0
PR interval NOS (msec) baseline <=200 and percent change >=50%	0	0	0	0	0	0	0	0	0	0	0	0	1
QRS interval not otherwise specified (NOS) (msec): baseline >100 and change from baseline >=25%	0	0	0	0	0	0	0	0	0	0	0	1	0
QRS interval not otherwise specified (NOS) (msec): baseline <=100 and change from baseline >=50%	0	0	0	0	0	1	0	0	0	0	0	0	0
QTcF NOS (msec): 450 <= value <=480	0	1	2	2	1	6	1	3	4	3	2	14	5
QTcF NOS (msec): 481 <= value <=500	0	0	0	0	0	0	0	0	0	0	0	1	2
QTcF NOS (msec): value >=501	0	0	0	0	0	0	0	0	1	0	0	0	1
QTcF NOS (msec): 30 <= change from baseline <=60	1	0	2	0	1	2	0	0	1	1	2	9	5
QTcF NOS (msec): change from baseline >60	0	0	0	0	0	0	0	0	1	0	0	1	2

PrimaryOverall Response Rate (ORR): Part 2

ORR: percentage of participants with confirmed complete response (CR) or partial response (PR). Response evaluation criteria in solid tumors (RECIST) v1.1: a) CR = disappearance of all non-nodal target lesions. In addition, any pathological lymph nodes assigned as target lesions that had a reduction in short axis to less than (\<) 10 millimeter (mm). Disappearance of all non-target lesions. In addition, all lymph nodes assigned a non-target lesion must be non-pathological in size (\<10 mm short axis) and b) PR = at least a 30 percent (%) decrease in the sum of diameter of all target lesions, taking as reference the baseline sum of diameters. Any radiological assessments taken more than 30 days after the last dose of study therapy or after antineoplastic agents other than study treatments taken by the participants was excluded from the best overall response derivation. Confirmation of CR or PR was to be at least 4 weeks apart from the previous radiological assessment.

Time frame:: From the start of the treatment until disease/clinical progression or death or early study discontinuation, whichever happened earlier (approximately up to 24 months)
Reported as:: Number · Percentage of participants

Overall Response Rate (ORR): Part 2
Percentage of participants	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Overall Response Rate (ORR): Part 2	6.7 (1.4 to 18.3)	22.7 (7.8 to 45.4)

SecondaryMaximum Observed Plasma Concentration (Cmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2

The maximum observed concentration of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. The Cmax value was observed directly from data.

Time frame:: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on Cycle 1 Day 1 (C1D1); Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D1
Reported as:: Geometric mean · Nanogram per milliliter

Maximum Observed Plasma Concentration (Cmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2
Nanogram per milliliter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Maximum Observed Plasma Concentration (Cmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2	5.39 ± NA	22.1 ± 31.9	29.1 ± 90.8	164.1 ± 37	243.5 ± 47	202.6 ± 47	388.1 ± 9	276.4 ± 42	393.8 ± 42	225.4 ± 28	228.5 ± 32	121.8 ± 54	43.51 ± 121	224.9 ± 43	181.4 ± 41

SecondaryTime to Reach Cmax at Steady State (Tmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2

Tmax of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported.

Time frame:: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D1
Reported as:: Median · Hour

Time to Reach Cmax at Steady State (Tmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2
Hour	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Time to Reach Cmax at Steady State (Tmax) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1 + Part 2	2.17 (2.17 to 2.17)	1.25 (0.500 to 2.00)	2.02 (2.00 to 2.03)	0.983 (0.500 to 1.90)	2.17 (1.10 to 5.47)	1.90 (0.517 to 3.00)	3.64 (2.00 to 5.92)	2.02 (0.517 to 6.00)	3.49 (0.550 to 6.03)	1.97 (0.533 to 5.95)	2.52 (0.500 to 3.00)	2.00 (0.517 to 10.3)	10.0 (5.35 to 10.2)	1.98 (1.00 to 4.17)	1.94 (0.967 to 5.50)

SecondaryArea Under the Concentration-Time Profile From Time 0 to the Time of the Last Quantifiable Concentration (AUClast) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1

AUClast of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Reported as:: Geometric mean · Hour*nanogram per milliliter

Area Under the Concentration-Time Profile From Time 0 to the Time of the Last Quantifiable Concentration (AUClast) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
Hour*nanogram per milliliter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Area Under the Concentration-Time Profile From Time 0 to the Time of the Last Quantifiable Concentration (AUClast) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1	18.3 ± NA	39.2 ± 58.3	96.6 ± 442	599.4 ± 53	1295 ± 25	787.9 ± 59	2510 ± 25	1395 ± 38	1976 ± 49	1034 ± 43	1040 ± 46	596.8 ± 33	192.0 ± 201

SecondaryArea Under the Concentration-Time Profile From Time 0 Extrapolated to Infinite Time (AUCinf) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1

AUCinf of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Reported as:: Geometric mean · Hour*nanogram per milliliter

Area Under the Concentration-Time Profile From Time 0 Extrapolated to Infinite Time (AUCinf) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
Hour*nanogram per milliliter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Area Under the Concentration-Time Profile From Time 0 Extrapolated to Infinite Time (AUCinf) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1	21.0 ± NA	45.2 ± NA	101 ± NA	648.4 ± 60	1492 ± 20	892.6 ± 73	2010 ± 3400	1614 ± 48	1875 ± 41	884.3 ± 34	1142 ± 50	593.3 ± 17	—

SecondaryApparent Clearance (CL/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1

CL/F of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Reported as:: Geometric mean · Liter per hour

Apparent Clearance (CL/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
Liter per hour	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Apparent Clearance (CL/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1	47.6 ± NA	44.2 ± NA	49.7 ± NA	15.43 ± 60	16.78 ± 20	28.04 ± 73	10.3 ± 17.4	21.70 ± 48	26.63 ± 41	28.26 ± 34	21.87 ± 50	42.14 ± 17	—

SecondaryApparent Volume of Distribution (Vz/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1

Vz/F of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Reported as:: Geometric mean · Liter

Apparent Volume of Distribution (Vz/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
Liter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Apparent Volume of Distribution (Vz/F) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1	111 ± NA	116 ± NA	141 ± NA	55.32 ± 28	61.33 ± 20	97.32 ± 56	55.5 ± 60.0	86.06 ± 37	79.74 ± 15	83.54 ± 17	72.18 ± 37	132.2 ± 52	—

SecondaryTerminal Half-life (t1/2) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1

t1/2 of PF-06873600 after single dose of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported.

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D1
Reported as:: Mean · Hour

Terminal Half-life (t1/2) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1
Hour	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release
Terminal Half-life (t1/2) of PF-06873600 Following a Single Oral Dose of Study Intervention on Cycle 1 Day 1 - Part 1	1.61 ± NA	1.82 ± NA	1.96 ± NA	2.567 ± 0.82033	2.540 ± 0.14394	2.446 ± 0.54574	2.39 ± 3.74	2.809 ± 0.59669	2.163 ± 0.74732	2.128 ± 0.73966	2.428 ± 0.87316	2.250 ± 0.77350	—

SecondarySteady State Maximum Concentration (Css,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2

Css,max of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Reported as:: Geometric mean · Nanogram per milliliter

Steady State Maximum Concentration (Css,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2
Nanogram per milliliter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Steady State Maximum Concentration (Css,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2	10.9 ± NA	18.2 ± 45.4	46.3 ± 126	124.3 ± 29	382.4 ± 33	246.4 ± 40	362 ± 399	290.2 ± 29	335.2 ± 22	305.0 ± 35	276.5 ± 31	82.11 ± 72	273.5 ± 35	250.5 ± 44

SecondaryTime to Maximum Plasma Concentration at Steady State (Tss,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2

Tss,max of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Reported as:: Median · Hour

Time to Maximum Plasma Concentration at Steady State (Tss,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2
Hour	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Time to Maximum Plasma Concentration at Steady State (Tss,Max) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2	1.00 (1.00 to 1.00)	1.25 (0.500 to 2.00)	1.20 (0.500 to 1.90)	2.00 (0.250 to 2.13)	1.95 (0.900 to 5.70)	1.92 (1.00 to 2.92)	2.01 (2.00 to 2.02)	2.23 (0.000 to 4.05)	1.98 (1.10 to 4.25)	1.88 (0.517 to 2.12)	2.08 (1.82 to 3.93)	2.99 (0.000 to 4.00)	1.95 (0.917 to 4.02)	1.97 (0.933 to 5.88)

SecondarySteady State Minimum Plasma Concentration (Css,Min) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2

Css,min of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B and Part 2) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Part 1: pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15; Part 2: pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Reported as:: Geometric mean · Nanogram per milliliter

Steady State Minimum Plasma Concentration (Css,Min) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2
Nanogram per milliliter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Steady State Minimum Plasma Concentration (Css,Min) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1 + Part 2	0.0000 ± NA	0.000 ± 0.000	1.19 ± 23.6	5.499 ± 5	37.63 ± 112	21.28 ± 130	52.1 ± 80.4	25.56 ± 8	25.63 ± 101	21.25 ± 106	13.33 ± 204	45.78 ± 49	23.67 ± 156	19.16 ± 131

SecondarySteady-State Area Under the Plasma Concentration Versus Time Curve Within One Dose Interval (AUCss,Tau) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1

AUCss,tau of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Reported as:: Geometric mean · Hour*nanogram per milliliter

Steady-State Area Under the Plasma Concentration Versus Time Curve Within One Dose Interval (AUCss,Tau) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
Hour*nanogram per milliliter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release
Steady-State Area Under the Plasma Concentration Versus Time Curve Within One Dose Interval (AUCss,Tau) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1	25.3 ± NA	51.4 ± 86.9	150 ± 483	448.8 ± 25	1695 ± 34	1010 ± 40	2060 ± 2360	1372 ± 39	1607 ± 34	1229 ± 41	1273 ± 50	636.8 ± 59

SecondarySteady-State Apparent Oral Plasma Clearance (CLss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1

CLss/F of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Reported as:: Geometric mean · Liter per hour

Steady-State Apparent Oral Plasma Clearance (CLss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
Liter per hour	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release
Steady-State Apparent Oral Plasma Clearance (CLss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1	39.5 ± NA	23.0 ± 38.9	10.4 ± 33.2	22.28 ± 24	14.78 ± 34	24.76 ± 40	14.8 ± 17.0	25.54 ± 39	21.99 ± 44	20.35 ± 41	19.63 ± 49	47.08 ± 59

SecondaryApparent Volume of Distribution at Steady State (Vss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1

Vss/F of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Reported as:: Geometric mean · Liter

Apparent Volume of Distribution at Steady State (Vss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
Liter	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release
Apparent Volume of Distribution at Steady State (Vss/F) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1	—	53.3 ± 98.4	124 ± NA	72.17 ± 19	57.62 ± 29	99.62 ± 35	70.8 ± NA	99.03 ± 48	75.41 ± 17	75.71 ± 32	80.33 ± 27	—

SecondaryAccumulation Ratio Based on AUC (Rac) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1

Rac of PF-06873600 after multiple doses of study intervention when given as a single agent (Part 1A and Part 1C), in combination with letrozole, and in combination with fulvestrant (Part 1B) was reported. Multiple-dose PK parameters were not calculated for the modified release selection cohort in Part 1C (ie, the group "Part 1C PF-06873600 MR 20 IR 25 mg BID").

Time frame:: Pre-dose, 0.25, 0.5, 1, 2, 3, 4, 6, 12 hours post-dose on C1D15
Reported as:: Geometric mean · Ratio

Accumulation Ratio Based on AUC (Rac) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1
Ratio	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 30 mg BID Long Release
Accumulation Ratio Based on AUC (Rac) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 1	1.210 ± NA	1.160 ± NA	1.53 ± NA	0.7263 ± 28	1.045 ± 17	1.254 ± 49	0.822 ± NA	0.8893 ± 32	1.260 ± 25	1.191 ± 29	1.268 ± 35	—

SecondaryAccumulation Ratio Based on Cmax (Observed) (Rac,Cmax) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 2

Rac,cmax of PF-06873600 after multiple doses of study intervention when given as in combination with fulvestrant (Part 2) was reported.

Time frame:: Pre-dose, 1, 2, 4, 6 hours post-dose on C1D15
Reported as:: Geometric mean · Ratio

Accumulation Ratio Based on Cmax (Observed) (Rac,Cmax) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 2
Ratio	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Accumulation Ratio Based on Cmax (Observed) (Rac,Cmax) of PF-06873600 Following Multiple Doses of Study Intervention on Cycle 1 Day 15 - Part 2	1.161 ± 78	1.381 ± 34

SecondaryPharmacodynamic (PD) Biomarker Phospho-retinoblastoma Protein (pRb) in Tumor Tissue in Participants - Part 1 + Part 2

Level of the PD marker, pRb, was analyzed at 2 time points, at screening and at Cycle 2 Day 1. Percentage changes of pRb at Cycle 2 Day 1 from screening (baseline) were calculated.

Time frame:: Screening and Cycle 2 Day 1
Reported as:: Median · Percentage of change

Pharmacodynamic (PD) Biomarker Phospho-retinoblastoma Protein (pRb) in Tumor Tissue in Participants - Part 1 + Part 2
Percentage of change	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Pharmacodynamic (PD) Biomarker Phospho-retinoblastoma Protein (pRb) in Tumor Tissue in Participants - Part 1 + Part 2	—	—	—	—	-84.44 (NA to NA)	-11.11 (-172.414 to 326.323)	—	—	—	—	-77.50 (NA to NA)	—	—	-30.43 (-103.371 to 184.820)	—

SecondaryPD Biomarker Ki67 in Tumor Tissue in Participants - Part 1 + Part 2

Level of the PD marker, Ki67, was analyzed at 2 time points, at screening and at Cycle 2 Day 1. Percent changes of pRb at Cycle 2 Day 1 from screening (baseline) were calculated.

Time frame:: Screening and Cycle 2 Day 1
Reported as:: Median · Percentage of change

PD Biomarker Ki67 in Tumor Tissue in Participants - Part 1 + Part 2
Percentage of change	Part 1A PF-06873600 1 mg BID	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
PD Biomarker Ki67 in Tumor Tissue in Participants - Part 1 + Part 2	—	—	—	—	-63.64 (NA to NA)	-6.67 (-99.910 to 138.742)	—	—	—	—	-90.00 (NA to NA)	—	—	-33.33 (-60.398 to 8.593)	—

Adverse events

Collected over Day 1 up to 28 days after the last dose of study intervention, up to approximately 36.6 months. Non-serious events are listed at a 5% frequency threshold.

Adverse event summary by group
Group	Deaths	Serious	Other
Part 1A PF-06873600 1 mg BID	0/1 (0%)	0/1 (0%)	1/1 (100%)
Part 1A PF-06873600 2 mg BID	0/2 (0%)	1/2 (50%)	2/2 (100%)
Part 1A PF-06873600 5 mg BID	0/2 (0%)	0/2 (0%)	2/2 (100%)
Part 1A PF-06873600 10 mg BID	0/3 (0%)	0/3 (0%)	3/3 (100%)
Part 1A PF-06873600 25 mg BID	1/9 (11.1%)	2/9 (22.2%)	9/9 (100%)
Part 1A PF-06873600 25 mg BID Biomarker	0/7 (0%)	0/7 (0%)	6/7 (85.7%)
Part 1A PF-06873600 35 mg BID	0/4 (0%)	1/4 (25%)	4/4 (100%)
Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	1/13 (7.7%)	4/13 (30.8%)	13/13 (100%)
Part 1A PF-06873600 50 mg BID	3/10 (30%)	6/10 (60%)	10/10 (100%)
Part 1B PF-06873600 25 mg BID IR/Fulvestrant Combination	1/9 (11.1%)	1/9 (11.1%)	9/9 (100%)
Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	0/7 (0%)	2/7 (28.6%)	7/7 (100%)
Part 1C PF-06873600 MR 20 mg IR 25 mg BID	0/5 (0%)	0/5 (0%)	5/5 (100%)
Part 1C PF-06873600 MR 30 mg BID Long Release	3/6 (50%)	3/6 (50%)	6/6 (100%)
Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	6/45 (13.3%)	9/45 (20%)	45/45 (100%)
Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination	4/28 (14.3%)	5/28 (17.9%)	25/28 (89.3%)

Most frequent serious events

Showing 10 of 44

Most frequent serious events
Event	Part 1A PF-06873600 1 mg BID	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
Intestinal obstructionGastrointestinal disorders	0/1	1/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	0/7	0/5	0/6	0/45	0/28
Febrile neutropeniaBlood and lymphatic system disorders	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	3/10	0/9	0/7	0/5	0/6	1/45	1/28
Abdominal painGastrointestinal disorders	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	3/10	0/9	0/7	0/5	0/6	0/45	0/28
PneumoniaInfections and infestations	0/1	0/2	0/2	0/3	0/9	0/7	1/4	0/13	0/10	0/9	0/7	0/5	0/6	0/45	0/28
StomatitisGastrointestinal disorders	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	0/7	0/5	1/6	1/45	0/28
HyperbilirubinaemiaHepatobiliary disorders	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	0/7	0/5	1/6	0/45	0/28
Neck painMusculoskeletal and connective tissue disorders	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	0/7	0/5	1/6	0/45	0/28
COVID-19Infections and infestations	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	1/7	0/5	0/6	0/45	0/28
Herpes zosterInfections and infestations	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	1/7	0/5	0/6	0/45	0/28
Ischaemic strokeNervous system disorders	0/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	0/9	1/7	0/5	0/6	0/45	0/28

Most frequent other events

Showing 10 of 177

Most frequent other events
Event	Part 1A PF-06873600 1 mg BID	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 MR 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination
AnaemiaBlood and lymphatic system disorders	0/1	0/2	0/2	0/3	5/9	1/7	4/4	4/13	6/10	5/9	5/7	3/5	3/6	21/45	11/28
Abdominal painGastrointestinal disorders	0/1	2/2	0/2	0/3	0/9	2/7	0/4	2/13	2/10	1/9	0/7	0/5	0/6	10/45	0/28
NauseaGastrointestinal disorders	0/1	0/2	2/2	0/3	6/9	5/7	0/4	9/13	6/10	6/9	5/7	2/5	4/6	30/45	20/28
Alanine aminotransferase increasedInvestigations	1/1	1/2	0/2	0/3	0/9	1/7	0/4	2/13	1/10	0/9	2/7	0/5	0/6	4/45	1/28
Aspartate aminotransferase increasedInvestigations	1/1	1/2	0/2	0/3	0/9	0/7	1/4	2/13	1/10	1/9	2/7	1/5	1/6	4/45	1/28
Neutrophil count decreasedInvestigations	0/1	0/2	0/2	0/3	2/9	1/7	4/4	2/13	2/10	2/9	5/7	3/5	4/6	18/45	4/28
Platelet count decreasedInvestigations	0/1	0/2	0/2	0/3	3/9	0/7	4/4	1/13	1/10	4/9	1/7	2/5	1/6	6/45	1/28
HyperphosphataemiaMetabolism and nutrition disorders	1/1	0/2	0/2	0/3	0/9	0/7	0/4	0/13	0/10	2/9	0/7	0/5	1/6	3/45	1/28
DizzinessNervous system disorders	0/1	0/2	0/2	1/3	0/9	1/7	3/4	1/13	2/10	1/9	0/7	0/5	0/6	12/45	1/28
AlopeciaSkin and subcutaneous tissue disorders	0/1	0/2	0/2	0/3	4/9	0/7	3/4	2/13	4/10	1/9	2/7	2/5	0/6	17/45	8/28

Baseline characteristics

Analysis population consisted of all enrolled participants who received at least 1 dose of study intervention.

Age, Categorical
Age, Categorical(Participants)	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination	Total
<=18 years	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Between 18 and 65 years	1	2	1	1	7	6	3	11	7	6	6	2	4	34	17	108
>=65 years	0	0	1	2	2	1	1	2	3	3	1	3	2	11	11	43

Sex: Female, Male
Sex: Female, Male(Participants)	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination	Total
Female	1	2	2	3	9	7	4	13	10	9	7	5	6	45	28	151
Male	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0

Ethnicity (NIH/OMB)
Ethnicity (NIH/OMB)(Participants)	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination	Total
Hispanic or Latino	0	0	0	0	0	1	2	2	1	0	1	0	0	5	0	12
Not Hispanic or Latino	1	2	2	3	8	6	2	10	9	7	6	4	6	37	27	130
Unknown or Not Reported	0	0	0	0	1	0	0	1	0	2	0	1	0	3	1	9

Race (NIH/OMB)
Race (NIH/OMB)(Participants)	Part 1A PF-06873600 1 mg Twice a Day (BID)	Part 1A PF-06873600 2 mg BID	Part 1A PF-06873600 5 mg BID	Part 1A PF-06873600 10 mg BID	Part 1A PF-06873600 25 mg BID	Part 1A PF-06873600 25 mg BID Biomarker	Part 1A PF-06873600 35 mg BID	Part 1A PF-06873600 35 mg Intermittent Dosing 5 Days on / 2 Days Off	Part 1A PF-06873600 50 mg BID	Part 1B PF-06873600 25 mg BID Immediate Release (IR)/Fulvestrant Combination	Part 1B PF-06873600 25 mg BID IR/Letrozole Combination	Part 1C PF-06873600 Modified Release (MR) 20 mg IR 25 mg BID	Part 1C PF-06873600 MR 30 mg BID Long Release	Part 2A PF-06873600 25 mg BID IR/Fulvestrant Combination	Part 2C PF-06873600 25 mg BID IR/Fulvestrant Combination	Total
American Indian or Alaska Native	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Asian	0	0	1	0	3	0	0	1	0	0	2	0	2	5	8	22
Native Hawaiian or Other Pacific Islander	0	0	0	0	0	1	0	0	0	0	0	0	0	0	0	1
Black or African American	0	0	0	0	1	0	0	2	1	0	0	0	2	4	0	10
White	1	2	1	3	4	6	3	8	8	9	4	5	2	32	20	108
More than one race	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Unknown or Not Reported	0	0	0	0	1	0	1	2	1	0	1	0	0	4	0	10

Study locations

54 sites

University of Alabama at Birmingham
Birmingham, Alabama 35233, United States
University Of Alabama at Birmingham
Birmingham, Alabama 35249, United States
HonorHealth
Scottsdale, Arizona 85258, United States
Virginia G. Piper Cancer Center Pharmacy
Scottsdale, Arizona 85258, United States
Highlands Oncology Group
Fayetteville, Arkansas 72703, United States
Highlands Oncology Group
Rogers, Arkansas 72758, United States
Highlands Oncology Group
Springdale, Arkansas 72762, United States
Highlands Oncology
Springdale, Arkansas 72762, United States
The Oncology Institute of Hope and Innovation
Glendale, California 91204, United States
The Oncology Institute of Hope and Innovation
Long Beach, California 90805, United States
UCSF Helen Diller Family Comprehensive Cancer Center
San Francisco, California 94143, United States
UCSF Investigational Drugs Pharmacy
San Francisco, California 94158, United States
The Oncology Institute of Hope and Innovation
Santa Ana, California 92705, United States
UCLA Hematology/Oncology - Parkside
Santa Monica, California 90404, United States
UCLA Hematology/Oncology - Santa Monica
Santa Monica, California 90404, United States
The Oncology Institute of Hope and Innovation
Whittier, California 90602, United States
University of Colorado Hospital - Anschutz Cancer Pavilion (ACP)
Aurora, Colorado 80045, United States
University of Colorado Hospital - Anschutz Inpatient Pavilion (AIP)
Aurora, Colorado 80045, United States
University of Colorado Hospital - Anschutz Outpatient Pavilion (AOP)
Aurora, Colorado 80045, United States
UCHealth Lone Tree Medical Center
Lone Tree, Colorado 80124, United States
Holy Cross Hospital
Fort Lauderdale, Florida 33308, United States
Massachusetts General Hospital
Boston, Massachusetts 02114, United States
Brigham & Women's Hospital
Boston, Massachusetts 02115, United States
Dana Farber Cancer Institute
Boston, Massachusetts 02215, United States
Dana-Farber Cancer Institute
Boston, Massachusetts 02215, United States
Memorial Sloan Kettering Cancer Center
Long Island City, New York 11101, United States
Memorial Sloan Kettering Cancer Center
New York, New York 10065, United States
Tennessee Oncology, PLLC
Nashville, Tennessee 37203, United States
The Sarah Cannon Research Institute-Pharmacy
Nashville, Tennessee 37203, United States
The Sarah Cannon Research Institute
Nashville, Tennessee 37203, United States
The University of Texas MD Anderson Cancer Center
Houston, Texas 77030, United States
South Texas Accelerated Research Therapeutics, LLC
San Antonio, Texas 78229, United States
Northwest Medical Specialties, PLLC
Federal Way, Washington 98003, United States
Northwest Medical Specialties, PLLC
Gig Harbor, Washington 98332, United States
Rainier Hematology-Oncology PC
Puyallup, Washington 98373, United States
Rainier Hematology-Oncology, PC
Puyallup, Washington 98373, United States
Fred Hutchinson Cancer Center
Seattle, Washington 98109, United States
University of Washington Medical Center
Seattle, Washington 98195, United States
Northwest Medical Specialties, PLLC
Tacoma, Washington 98405, United States
Multiprofile Hospital of Active Treatment - Dobrich AD
Dobrich, 9300, Bulgaria
Specialized Hospital for Active Treatment of Oncology - Haskovo EOOD
Haskovo, 6300, Bulgaria
Complex Oncology Center -Plovdiv
Plovdiv, 4000, Bulgaria
McGill University Health Centre
Montreal, Quebec H4A 3J1, Canada
National Cancer Center Hospital East
Kashiwa, Chiba 277-8577, Japan
Kanagawa cancer center
Yokohama, Kanagawa 2418515, Japan
Private Medical Institution "Euromedservice"
Pushkin, Sankt-Peterburg 196603, Russia
BIH of Omsk Region "Clinical Oncological Dispensary"
Omsk, 644013, Russia
BIH of Omsk Region "Clinical Oncological Dispensary"
Omsk, 644046, Russia
LLC "Medicina Severnoy Stolitsy"
Saint Petersburg, 191025, Russia
LLC "Severo-Zapadny Medical Center"
Saint Petersburg, 192007, Russia
Municipal Non-profit Enterprise "City Clinical Hospital #4" of Dnipro City Council, "Dnipro State Me
Dnipro, Dnipropetrovsk Oblast 49102, Ukraine
Kharkiv Regional Specialized Dispensary of Radiation Protection of the Population
Kharkiv, Kharkiv Oblast 61166, Ukraine
Communal nonprofit enterprise "Kyiv City Clinical Oncology Center" of Executive Body of Kyiv City
Kyiv, 03115, Ukraine
Communal noncommercial enterprise of Lviv regional council "Lviv oncological regional therapeutical
Lviv, 79031, Ukraine

References and documents

Study documents

Study protocol · Mar 3, 2023
Statistical analysis plan · Mar 23, 2023

Documents are hosted by the registry — open the source record to download them.

Individual participant data

Plan to share: Yes — Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.

Updates

Tracking since Sep 25, 2026

No changes since tracking began. The registry record was last updated on Nov 14, 2025, before this site started recording changes on Sep 25, 2026. Its history is on ClinicalTrials.gov ↗

Registry details

Key details

Study ID: NCT03519178
Lead sponsor: Pfizer
Responsible party: Sponsor
First posted: May 8, 2018
Start date: Mar 7, 2018
Primary completion: Apr 5, 2023
Completion: Oct 30, 2024
Results posted: Jul 31, 2024
Last update: Nov 14, 2025

Study contacts

Pfizer CT.gov Call Center

study director · Pfizer

Oversight

Data monitoring committee: No
FDA-regulated drug: Yes
FDA-regulated device: No

View the source record on ClinicalTrials.gov ↗

Not currently enrolling

This study is terminated, as verified in Oct 2025. You cannot join it, but the record below documents what was studied.

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Discussion

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