A Phase 3 interventional study of PF-07248144 and Fulvestrant in Breast Cancer, sponsored by Pfizer. Recruiting at 433 sites in 31 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-10-19.
Sponsored by Pfizer · Phase 3, Interventional, and Treatment
The purpose of this study is to learn about the safety and effects of the study medicine PF-07248144 when given along with fulvestrant for the possible treatment of HR-positive, HER2-negative advanced or metastatic breast cancer.
HR-positive breast cancer cells have proteins on their surface called receptors that bind to hormones like estrogen and progesterone (female sex hormones). These hormones can promote the growth of cancer cells.
HER2-negative describes cells that have a small amount or none of a protein called HER2 on their surface. In normal cells, HER2 helps control cell growth. Cancer cells that are HER2-negative may grow more slowly and are less likely to recur (come back) or spread to other parts of the body than cancer cells that have a large amount of HER2 on their surface.
Advanced cancer is a term that is often used to describe cancer that is unlikely to be cured.
Metastatic cancer is the type where the cancer cells spread from one part of the body to another.
This study is seeking for participants whose breast cancer has gotten worsen after receiving cyclin dependent kinase (CDK) 4/6 inhibitor-based therapy.
Half of participants in this study will receive their usual study treatment, everolimus with endocrine therapy (either exemestane or fulvestrant) for HR-positive/HER2-negative advanced or metastatic breast cancer (A/mBC). The study doctor will discuss which hormone therapy is right for the participant before treatment begins.
PF-07248144 is a tablet that will be taken by mouth at home every day in a 28-day cycle. Fulvestrant will be given as two injections (one injection in the buttock) at visits to the study clinic. Everolimus and exemestane are also tablets and will be taken by mouth at home every day in a 28-day cycle.
The study will compare the experiences of people receiving PF-07248144 in combination with fulvestrant to those of the people who do not. This will help see if PF-07248144 in combination with fulvestrant is safe and effective.
14,825 studies on the registry are indexed under Breast Neoplasms; 3,319 are open to participants now.
This study's planned enrollment of 400 is above the median of 72 across 10,896 interventional studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →Pfizer is the lead sponsor of 3,334 studies on the registry; 149 are open to participants now.
Of its 601 completed or terminated interventional studies of FDA-regulated products, 391 (65%) have results posted.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
The amount of disease can be tracked with a defined measurement, so the study can see whether it shrinks or grows. It might be a tumour measured on a scan or, in some blood cancers such as myeloma, a marker measured in blood or urine.
The criteria or the study team say which measurement counts — having no tumour visible on a scan does not by itself rule you out.
The standard rules for measuring tumours on CT or MRI scans, to tell whether a cancer is shrinking, stable or growing during treatment.
“Measurable disease per RECIST 1.1” usually means at least one tumour 10 mm or more at its longest on a CT scan, or a lymph node 15 mm or more across its short axis.
A scale of how much an illness limits everyday activity. For people being assessed to join a study, scores run from 0 (fully active) to 4; lower is more active.
Studies most often ask for 0–1 or 0–2. Your doctor gives the score; the WHO scale uses the same steps. The full scale also has 5, which records death.
A line of therapy is one course of treatment, which may combine several drugs. First-line is the first course given; second-line follows when that stops working or is not tolerated.
“Two prior lines” means two courses that count separately under the study’s rules — not simply two drugs. Ask the study team if you are unsure how yours are counted.
HER2
HER2 is a protein, made from the ERBB2 gene, that drives the growth of some cancers. A study may look for a level of the protein, extra copies of the gene, or a particular change in it.
In breast cancer, protein tests are read as HER2-positive, HER2-low or HER2-negative; other cancers use their own rules. Check which test result the study requires.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Metastases
Cancer that has spread from where it began to other parts of the body. “Metastatic” cancer is cancer that has spread this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Adjuvant and neoadjuvant
Neoadjuvant treatment is given before the main treatment (usually surgery), often to shrink a tumour. Adjuvant treatment is given after it, to lower the chance of the cancer coming back.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Measurable disease
The amount of disease can be tracked with a defined measurement, so the study can see whether it shrinks or grows. It might be a tumour measured on a scan or, in some blood cancers such as myeloma, a marker measured in blood or urine.
The criteria or the study team say which measurement counts — having no tumour visible on a scan does not by itself rule you out.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
RECIST
The standard rules for measuring tumours on CT or MRI scans, to tell whether a cancer is shrinking, stable or growing during treatment.
“Measurable disease per RECIST 1.1” usually means at least one tumour 10 mm or more at its longest on a CT scan, or a lymph node 15 mm or more across its short axis.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
ECOG performance status
A scale of how much an illness limits everyday activity. For people being assessed to join a study, scores run from 0 (fully active) to 4; lower is more active.
Studies most often ask for 0–1 or 0–2. Your doctor gives the score; the WHO scale uses the same steps. The full scale also has 5, which records death.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Line of therapy
A line of therapy is one course of treatment, which may combine several drugs. First-line is the first course given; second-line follows when that stops working or is not tolerated.
“Two prior lines” means two courses that count separately under the study’s rules — not simply two drugs. Ask the study team if you are unsure how yours are counted.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
PF-07248144 tablet taken by mouth plus fulvestrant taken as a shot into the muscle.
Drug: PF-07248144 · Drug: Fulvestrant
Everolimus tablet taken by mouth plus investigator's choice of endocrine therapy of exemestane tablet taken by mouth or fulvestrant taken as a shot into the muscle.
Drug: Fulvestrant · Drug: Everolimus · Drug: Exemestane
KAT6 inhibitor
Endocrine therapy
mTOR inhibitor
Endocrine therapy
Progression Free Survival (PFS) as determined by blinded independent central review (BICR) per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1
Time frame: From the date of randomization until disease progression or death due to any cause (up to approximately 2 years)
Overall Survival (OS)
Time frame: From the date of randomization until death due to any cause (up to approximately 5 years).
Number of Participants with Objective Response (OR) by BICR
Time frame: From the date of randomization until disease progression or death due to any cause (up to approximately 2 years)
Duration of Response (DoR) as defined by BICR
Time frame: From the date of the first objective (PR or CR) response (every 8 weeks during the first 48 weeks and then every 12 week) up to approximately 2 years.
Number of Participants With Clinical Benefit Response (CBR) by BICR
Time frame: From randomization date (every 8 weeks during the first 48 weeks and then every 12 weeks) up to approximately 2 years.
Number or Patients with Adverse Events (AEs) by Type
Time frame: From screening until 28 days after the last dose, to approximately 5 years
Number or Patients with AEs by Incidence
Time frame: From screening until 28 days after the last dose, to approximately 5 years
Number or Patients with AEs by Seriousness
Time frame: From screening until 28 days after the last dose, to approximately 5 years
Number or Patients with AEs by relationship to study interventions
Time frame: From screening until 28 days after the last dose, to approximately 5 years
Number of Participants With Abnormal Electrocardiogram (ECG; Arm A and B)
Time frame: From screening until 28 days after the last dose, to approximately 5 years
Number of Participants With Increase From Baseline in Corrected QT (QTc) Interval (Arm A only)
The study includes a QTc sub-study in approximately 40 participants in Arm A enrolled at selected sites which will evaluate the effect of PF-07248144 on QTc interval via collection of triplicate ECGs (central reading) time-matched with pharmacokinetic (PK) draws.
Time frame: 0h pre-dose on Cycle 1 Day 1, Cycle 1 Day 15, Cycle 2 Day 1, and Cycle 3 Day 1; additional 4 hrs post dose on Cycle 1 Day 15 and Cycle 2 Day 1
Number of Participants With Laboratory Test Abnormalities
Time frame: From screening until 28 days after the last dose, to approximately 5 years
Ctrough of PF-07248144
Ctrough was defined as pre-dose serum concentration during multiple dosing and observed directly from data.
Time frame: Cycle 1 (Day 1), Cycle 1 (Day 15), Cycle 2 (Day 1), and Cycles 3, 5, and 7 (Day 1) only. Each Cycle is 28 days
Showing the first 100 of 433 sites across 31 countries. Choose a country and city above to see the rest.
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.
Data sharing details ↗ · www.pfizer.com
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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Studies of the drugs tested here: Prifetrastat · Everolimus