PIK3CA-Related Overgrowth Spectrum Clinical Trials

• Women or men with histologically or cytologically confirmed carcinoma of the breast that is locally advanced or metastatic and is not amenable to surgical or radiation therapy with curative intent

• Documented estrogen receptor (ER)-positive and/or progesterone receptor (PR)-positive tumor according to American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) guidelines, defined as \>=1% of tumor cells stained positive based on the most recent tumor biopsy and assessed locally (Allison et al. 2020)

• Participants must not have received any prior systemic therapy for locally advanced unresectable or metastatic breast cancer (mBC) and must have progressed during adjuvant endocrine-based treatment or within 12 months after completing adjuvant endocrine-based therapy with an aromatase inhibitor or tamoxifen

• Confirmed biomarker eligibility as documented through central laboratory testing of a tumor tissue sample documenting both the lack of a phosphatidylinositol-4,5-biphosphate 3-kinase catalytic subunit alpha gene (PIK3CA) mutation and the presence of heterozygous loss of chromosome 8p (i.e., PIK3CAnmd and chr8p loss)

• Measurable disease per Response Evaluation Criteria in Solid Tumors, Version 1.1 (RECIST v1.1)