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

Inclusion Criteria: * 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 Exclusion Criteria: * Participants with advanced, symptomatic visceral spread, that are at risk of life-threatening complications in the short term * 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 * Inadequate l…