A Study to Learn About a New Medicine Called Vepdegestrant (ARV-471, PF-07850327) in People Who Have Advanced Metastatic Breast Cancer

Prior treatment

• Prior treatment with:
• ARV-471, fulvestrant, elacestrant, mTOR, PI3K, AKT pathway inhibitors, PARP inhibitor for any setting
• other investigational agents (including novel endocrine therapy any SERDs, SERCAs, CERANs) for any setting
• prior chemotherapy for advanced/metastatic disease
• Participants with significant concomitant illness

Other

• Participants with advanced, symptomatic visceral spread, that are at risk of life-threatening complications in the short term
• Inadequate liver, kidney and bone marrow function
• Active brain metastases

• Adult participants with loco-regional recurrent or metastatic breast disease not amenable to surgical resection or radiation therapy
• Confirmed diagnosis of ER+/HER2- breast cancer
• Prior therapies for locoregional recurrent or metastatic disease must fulfill all the following criteria:
• One line of CDK4/6 inhibitor therapy in combination with endocrine therapy. Only one line of CDK4/6 inhibitor is allowed in any setting.
• ≤ 1 endocrine therapy in addition to CDK4/6 inhibitor with ET
• Most recent endocrine treatment duration must have been given for ≥6 months prior to disease progression. This may be the endocrine treatment component of the CDK4/6 inhibitor line of therapy.
• Radiological progression during or after the last line of therapy.
• 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 0-1
• Participants should be willing to provide blood and tumor tissue