A Phase 1/2 interventional study of ARV-471 and Abemaciclib in Breast Cancer, sponsored by Pfizer. Active, not recruiting at 37 sites in 4 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-09-02.
Sponsored by Pfizer · Phase 1/2, Interventional, and Treatment
The purpose of this clinical trial is to learn about the safety and effects of the study medicine (called ARV-471) when given together with other medicines for the potential treatment of advanced or metastatic breast cancer.
This study is seeking participants who have breast cancer that:
For Sub-Study A:
All participants will receive ARV-471 and a medicine called abemaciclib. ARV-471 will be given by mouth, at home, 1 time a day. Abemaciclib will be given by mouth, at home, 2 times a day. We will examine the experiences of people receiving the study medicines. This will help us determine if the study medicines are safe and effective.
Participants will continue to take ARV-471 and abemaciclib until their cancer is no longer responding, or side effects become too severe. They will have visits at the study clinic about every 4 weeks.
C4891006 is a sub-study from the Umbrella platform, TACTIVE-U, comprising multiple sub-studies that independently evaluate ARV-471 in participants with Estrogen Receptor Positive (ER+) Advanced or Metastatic Breast Cancer (A/MBC). ARV-471 will act as the backbone therapy given in combination with other anticancer agents thought to have clinical relevance in ER+ breast cancer.
12,544 studies on the registry are indexed under Breast Neoplasms; 2,892 are open to participants now.
This study's enrollment of 37 is below the median of 72 across 9,303 interventional studies indexed under Breast Neoplasms.
Browse Breast Neoplasms studies →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.
Exclusion Criteria:
ARV-471 administered orally once daily (QD) and Abemaciclib orally twice daily (BID) on 28-day cycle
Drug: ARV-471 · Drug: Abemaciclib
Daily oral dosages of ARV-471 continuously, dose escalation/de-escalation in Phase 1b until the recommended phase 2 dose (RP2D) determined, cycles lasting 28 days
Also known as: vepdegestrant, PF-07850327
Daily oral dosages of Abemaciclib continuously, cycles lasting 28 days
Phase 1b: number of participants with dose limiting toxicities
Dose Limiting Toxicities rate for ARV-471 in combination with abemaciclib, estimated based on data from DLT-evaluable participants during the DLT observation period (Cycle 1 \[28 days\]).
Time frame: 28 days
Phase 2: percentage of participants with objective response by investigator assessment
Objective response (OR) refers to confirmed complete response (CR) or partial response (PR) according to Response Evaluation Criteria in Solid Tumor (RECIST) version 1.1. as determined by investigator assessment.
Time frame: Up to approximately 1 year
Phase 1b and Phase 2: number of participants experiencing any AE, SAE, Treatment Related SAE
An adverse event (AE) were any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. An SAE is any untoward medical occurrence that, at any dose: resulted in death; required inpatient hospitalization or prolongation of existing hospitalization; was life-threatening; resulted in persistent or significant disability/ incapacity; congenital anomaly/birth defect and other important medical events. Treatment-related AE is any untoward medical occurrence attributed to study drug in a participant who received study drug. AEs were graded by the investigator according to the Common Terminology Criteria for Adverse Events (CTCAE version 5.0) and coded using MedDRA were reported. Grade 1=mild; Grade 2=moderate; Grade 3=severe and Grade 4=life-threatening or disabling and grade 5=death.
Time frame: Up to 28 days after last dose of study treatment
Phase 1b and Phase 2: number of participants with lab abnormalities - Hematology and coagulation parameters
Blood samples were collected for the analysis of following hematology and coagulation parameters: hemoglobin \[g/L\], platelets, leukocytes, neutrophils, lymphocytes, monocytes, eosinophils and basophils \[10\^9/L\]; partial thromboplastin time prolonged, international normalized ratio increased, prothrombin time. Number of participants with hematological and coagulation abnormalities by grade as per CTCAE version 5.0 were reported. Grade 1=mild; Grade 2=moderate; Grade 3=severe and Grade 4=life-threatening or disabling and grade 5=death. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, abnormal, or not done.
Time frame: Up to 28 days after last dose of study treatment
Phase 1b and Phase 2: number of participants with lab abnormalities - chemistry parameters
Blood samples were collected for analysis of clinical chemistry parameters. These included: alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, \[international unit per liter (IU/L)\] ; Lipase and amilase \[IU/L\] (limited to cycle1 only); Albumin, bilirubin, urea ,calcium, creatinine, glucose, magnesium, phosphate, uric acid, chloride, potassium and sodium \[millimol per liter (mmol/L)\]; eGFR \[milliliter per minute (ml/min)\]. Number of participants with blood chemistry abnormalities by grade as per CTCAE version 5.0 were reported. Grade 1=mild; Grade 2=moderate; Grade 3=severe and Grade 4=life-threatening or disabling and grade 5=death. For laboratory tests without CTCAE grade definitions, results will be categorized as normal, abnormal, or not done.
Time frame: Up to 28 days after last dose of study treatment
Phase 1b: percentage of participants with objective response by investigator assessment
Objective response (OR) refers to confirmed complete response (CR) or partial response (PR) according to Response Evaluation Criteria in Solid Tumor (RECIST) version 1.1. as determined by investigator assessment.
Time frame: Up to approximately 1 year
Phase 1b and Phase 2: duration of response by investigator assessment.
Duration of Response (DoR) is defined for participants with confirmed OR (CR or PR) as the time from the first documentation of OR to the first documentation of objective tumor progression or to death due to any cause, whichever occurs first.
Time frame: Up to approximately 3 years
Phase 1b and Phase2: Percentage of participants with Clinical Benefit Response by investigator assessment.
Clinical Benefit Response (CBR) is defined as the proportion of participants with Best Overall Response of confirmed CR or PR at any time, or Stable Disease (SD) ≥24 weeks
Time frame: Up to approximately 1 year
Phase 1b and Phase 2: Progression Free Survival by investigator assessment.
Progression Free Survival (PFS) is defined as the time from the date of first dose of study interventions to the date of first documentation of PD or death due to any cause, whichever occurs first.
Time frame: Up to approximately 3 years
Phase 2: Overall Survival
Overall Survival (OS) is defined as the time from the date of first dose of study interventions to the date of death due to any cause
Time frame: Through study completion, up to approximately 3 year
Phase 2:ctDNA plasma quantitative changes from pre-treatment
To assess changes from baseline levels in plasma circulating DNA (ctDNA) with treatment and to evaluate potential predictability of their associations with clinical outcome
Time frame: Day 1, 29 and 57 and End of Treatment (an average of 1 year)
Phase 1b: Area Under the Curve from Time Zero to end of dosing interval Evaluation of abemaciclib with or without ARV-471
Exposure (AUCtau) of abemaciclib with and without co-administration of ARV-471
Time frame: Phase 1b: pre-dose Day -1, 1, 15, 29, 43, 57, 113, 169; 1, 2, 4, 6, 8 hours post dose on Day -1 and 15; post dose Day 29 and 43
Phase 1b: Maximum Observed Plasma Concentration (Cmax) of abemaciclib with or without ARV-471
Concentration (Cmax) of abemaciclib with and without co-administration of ARV-471
Time frame: Phase 1b: pre-dose Day -1, 1, 15, 29, 43, 57, 113, 169; 1, 2, 4, 6, 8 hours post dose on Day -1 and 15; post dose Day 29 and 43
Phase 1b and Phase 2: Maximum Observed Plasma Concentration (Cmax) of ARV-471
Plasma concentration of ARV-471
Time frame: Phase 1b: pre-dose Day 1, 15, 29, 43, 57, 113, 169; 1, 2, 4, 6, 8 hours post dose on Day 15; post dose Day 29 and 43. Phase 2: pre and post dose Day 15, 29 and 43; pre - dose Day 57, 113 and 169
Phase 1b and Phase 2: Maximum Observed Plasma Concentration (Cmax) of abemaciclib
Plasma concentration of abemaciclib
Time frame: Phase 1b: pre-dose Day -1, 1, 15, 29, 43, 57, 113, 169; 1, 2, 4, 6, 8 hours post dose on Day -1 and 15; post dose Day 29, 43 and 57 Phase 2: pre and post dose Day 15, 29 and 43; pre - dose Day 57, 113 and 169
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.
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