A Phase 3 Randomized, Double-Blind, Active-ControlledStudy of Palazestrant with Ribociclib Versus Letrozole with Ribociclib for the First-Line Treatment of ER+, HER2Advanced Breast Cancer (OPERA-02)

Palazestrant (OP-1250) is a pill designed to block and break down estrogen receptors, which are often what help certain breast cancers grow. It is being developed to treat people with a type of breast cancer that is estrogen‑receptor positive (ER+) and human epidermal growth factor receptor 2 (HER2)-negative. This study aims to compare two treatment combinations for people receiving their first treatment for ER+, HER2- breast cancer that has spread or cannot be removed with surgery. The study will look at how safe and effective palazestrant plus ribociclib is compared with letrozole plus ribociclib. Palazestrant is an experimental treatment. This means that it is not approved by the United States Food and Drug Administration (FDA).

Are you Eligible? (Inclusion Criteria)

• Adult Participant is ≥ 18 years 2. The person must have breast cancer that has been confirmed by lab testing, and the cancer has spread in the breast area or to other parts of the body. It cannot be cured with current treatments. They must also meet one of the following: a. They were diagnosed with advanced breast cancer from the start (this also includes people whose cancer came back even though they never had hormone‑blocking treatment after their first diagnosis). b. Their breast cancer came back more than 12 months after they finished hormone‑blocking treatment (this may or may not have included CDK4/6 inhibitor medicines).