A Phase 3 interventional study of PF-07248144 and Fulvestrant in Breast Cancer, sponsored by Pfizer. Recruiting at 202 sites in 27 countries. Open to participants aged 18 Years and older. Per ClinicalTrials.gov, last updated 2026-05-06.
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.
Exclusion Criteria:
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 202 sites across 27 countries.
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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