A Study of Tersolisib (LY4064809/STX-478) With Other Anti-Cancer Treatments in Participants With Advanced Breast Cancer With a Genetic Change (PIK3CA)

Inclusion Criteria: * Are willing to follow contraception requirements. Contraceptive use by participants should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies. * If assigned female at birth, pre-/peri- and postmenopausal status is allowed. Those with pre- or peri-menopausal status at study entry must agree to use ovarian function suppression with any locally approved gonadotropin-releasing hormone (GnRH) agonist. * If assigned male at birth with an estrogen receptor positive (ER+) breast cancer diagnosis, they must agree to use hormone suppression with a GnRH agonist. * Have histologically or cytologically confirmed breast cancer, defined as individuals with * locally advanced breast cancer not amenable to curative therapy (for example, surgery) or metastatic disease, and * hormone receptors (HR)+/human epidermal growth factor receptor 2 (HER2)- or HR+/HER low defined by American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) Guidelines * HR status: Documented ER+ and/or progesterone receptor-positive (PR+) tumor according to ASCO/CAP Guidelines, defined as greater than or equal to (≥)1 percent (%) of tumor cells stained positive based on the most recent tumor biopsy and assessed locally * HER status: immunohistochemistry score of 1+ or score of 2+ with a negative Fluorescence In Situ Hybridization (FISH) based on local results as defined in the ASCO/CAP Guidel…