A Study to Learn About the Study Medicine Called PF-07248144 in Combination With Fulvestrant in People With HR-positive, HER2-negative Advanced or Metastatic Breast Cancer Who Progressed After a Prior Line of 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…

• : * Confirmed diagnosis of HR-positive HER2-negative breast cancer with evidence of locally advanced or metastatic disease, which is not amenable to surgical resection or radiation therapy with curative intent. * Prior CDK4/6 inhibitor therapy in combination with endocrine therapy in advance metastatic setting or in adjuvant setting with documented progression during or within 12 months after the last dose of CDK4/6i. * Participants are eligible if they previously received CDK4/6i or ET as a monotherapy, or in combination for rechallenge therapy in the advance or metastatic setting; have received prior therapy targeting estrogen receptor 1 (ESR1) or breast cancer gene (BRCA)1/2. * Measurable disease evaluable per Response Evaluation Criterion in Solid Tumors (RECIST) v.1.1 or non-measurable bone-only disease * Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) 0 or 1.

Use the source registry for the full inclusion and exclusion criteria before discussing referral or enrolment.