This phase 3 clinical trial compares the safety and efficacy of palazestrant (OP-1250) to the standard-of-care options of fulvestrant or an aromatase inhibitor in women and men with breast cancer whose disease has advanced on one endocrine therapy in combination with a CDK4/6 inhibitor.

This is a Phase 1b open-label, 2-part study in 3 treatment groups. The 3 treatment groups are as follows:

Treatment Group 1: Palazestrant (OP-1250) in combination with ribociclib (KISQALI, Novartis Pharmaceuticals Corporation).

Treatment Group 2: Palazestrant (OP-1250) in combination with alpelisib (PIQRAY, Novartis Pharmaceuticals Corporation).

Treatment Group 3: Palazestrant (OP-1250) in combination with everolimus.

Treatment Group 4: Palazestrant (OP-1250) in combination with atirmociclib.