A Study to Learn About Vepdegestrant When Given With PF-07220060 to People With Advanced or Metastatic Breast Cancer.

Inclusion Criteria: * Histological or cytological diagnosis of breast cancer. At time of enrollment this must not be amenable to surgical resection with curative intent (≥1% ER+ stained cells as per local practice on the most recent tumor biopsy HER2- tumor by IHC or in-situ hybridization per ASCO/CAP). * prior anticancer therapies: Phase 1b: at least 1 line of SOC for A/MBC; Prior fulvestrant allowed; ≤1 prior chemotherapy line (no antibody-drug conjugates permitted) for A/MBC setting allowed. Phase 2: At least one and maximum 2 lines of ET in A/MBC setting and most recent ET-based regimen for \>6 months. 1, and only 1, prior CDK4/6 inhibitor-based regimen required. Up to 1 prior regimen of cytotoxic chemotherapy (no antibody-drug conjugates permitted) in the A/MBC setting; Prior fulvestrant allowed. * Participant with only non-measurable lesion (Phase1b) or at least 1 measurable lesion as defined by RECIST v1.1. (Phase2) are eligible. * ECOG PS = 0 or 1 (Phase1b) ; ≤2 (Phase2) Exclusion Criteria: * visceral crisis at risk of life-threatening complications in the short term. * Any condition precluding an adeguate absorption of study interventions. * newly diagnosed brain metastases, or symptomatic central nervous system (CNS) metastases, carcinomatous meningitis, or leptomeningeal disease. Participants with a history of CNS metastases or cord compression are eligible if they have been definitively treated, clinically stable and discontinued anti-seizure medications and…