A Phase 3 Open-label Randomized Study Assessing the Efficacy and Safety of RLY-2608 + Fulvestrant Versus Capivasertib +Fulvestrant as Treatment for PIK3CA-mutant Hormone ReceptorPositive, Human Epidermal Growth Factor Receptor 2 Negative(HR+/HER2-)

This study is being done to see how well a new, experimental drug called RLY-2608, when used together with another drug called fulvestrant, works compared to a currently approved treatment (capivasertib + fulvestrant) for a specific type of breast cancer. It’s for people who have hormone receptor-positive, HER2-negative breast cancer that has either spread in the body (metastatic) or grown into nearby tissues (locally advanced), and who also have a change (mutation) in a gene called PIK3CA.

Are you Eligible? (Inclusion Criteria)

• ≥18 years of age. 2.Women in the study can be postmenopausal, perimenopausal, or premenopausal.Postmenopausal women must meet one of the following conditions: - They are 60 years or older and have not had a period for at least 1 year, or They are under 60 years old, have not had a period for at least 1 year, and have stopped all hormone treatments, chemotherapy, or similar medications. Blood tests must show hormone levels consistent with menopause,or They have had both ovaries surgically removed. 3. Premenopausal or perimenopausal women must meet this condition:They must have started treatment with a GnRH agonist (a medication that suppresses hormone production) at least 4 weeks ago.