A Study to Evaluate the Efficacy and Safety of Giredestrant in Combination With Phesgo (Pertuzumab, Trastuzumab, and Hyaluronidase-zzxf) Versus Phesgo in Participants With Locally Advanced or Metastatic Breast Cancer (heredERA Breast Cancer)

Inclusion Criteria: * Histologically or cytologically confirmed and documented human epidermal growth factor receptor 2 (HER2)-positive/estrogen receptor (ER)-positive adenocarcinoma of the breast with metastatic or locally-advanced disease not amenable to curative resection * At least one measurable lesion and/or non-measurable disease evaluable according to Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 * Disease-free interval from completion of adjuvant or neoadjuvant systemic non-hormonal treatment to recurrence of ≥6 months * Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1 * Left ventricular ejection fraction (LVEF) of at least (≥)50% measured by echocardiogram (ECHO) or multiple-gated acquisition scan (MUGA) * Adequate hematologic and end-organ function * For women of childbearing potential: Participants who agree to remain abstinent (refrain from heterosexual intercourse) or use contraception, and agree to refrain from donating eggs, during the treatment period and for 7 months after the final dose of Phesgo * For men: participants who agree to remain abstinent (refrain from heterosexual intercourse) or use a condom, and agree to refrain from donating sperm, during the treatment period and for 7 months after the final dose of Phesgo to avoid exposing the embryo Maintenance Phase Inclusion Criteria * Complete a minimum of four cycles to a maximum of eight cycles of induction therapy; the minimum cycles are defined as either: Phe…