VIKTORIA-1 / CELC-G-301

This is a Phase 3, open-label, randomized clinical trial evaluating the efficacy and safety of gedatolisib plus fulvestrant with or without palbociclib for the treatment of patients with advanced (inoperable) or metastatic Hormone Receptor Positive, Human Epidermal Growth Factor Receptor 2 Negative (HR+/HER2-) breast cancer following progression on or after CDK4/6 and aromatase inhibitor therapy. Gedatolisib is an intravenously administered pan-PI3K/mTOR inhibitor. Palbociclib is a CDK4/6 inhibitor. Fulvestrant is a selective estrogen receptor degrader (SERD). Subjects will be assessed for PIK3CA status and then randomized to treatment arms according to their confirmed PIK3CA mutation status.