TACTIVE-U: A Study to Learn About the Study Medicine (Called ARV-471) When Given With Other Medicines in People With Advanced or Metastatic Breast Cancer (Sub-Study A)

Inclusion Criteria:

histological or cytological diagnosis of ER+ and HER2- advanced/metastatic breast cancer that is not amendable to surgical resection with curative intent (≥1% ER+ stained cells on the most recent tumor biopsy).
prior anticancer therapies: up to 2 lines of prior therapies for advanced/metastatic disease; 1 line of any CDK4/6 inhibitor-based regimen is required (independent of the setting eg, adjuvant or advanced/metastatic)
at least 1 measurable lesion as defined by RECIST v1.1.
ECOG PS ≤1.

Exclusion Criteria:

visceral crisis at risk of life-threatening complications in the short term
known history of drug-induced pneumonitis or other significant symptomatic deterioration of lung functions.
newly diagnosed brain metastases, or symptomatic 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 corticosteroids for at least 14 days prior to enrollment in the study.
history of any other tumor malignancies within the past 3 years, except for the following: (1) adequately treated basal or squamous cell carcinoma of the skin; (2) curatively treated in situ carcinoma of the cervix.
inflammatory breast cancer
impaired cardiovascular function or clinically significant cardiovascular diseases
concurrent administration of medications, food, or herb supplements that are strong inhibitors and strong/moderate inducers of CYP3A and drugs known to predispose to Torsade de Pointes or QT interval prolongation.
renal impairment, not adequate liver function and/or bone marrow function
known active infection