Palazestrant in Combination With Ribociclib for the First-line Treatment of ER+/HER2- Advanced Breast Cancer

Inclusion Criteria

• Adult female or male participants.
• ER+, HER2- locally advanced or metastatic breast cancer that is not amenable to curative therapy.
• Evaluable disease (measurable disease per RECIST 1.1 or bone-only disease).
• De novo advanced breast cancer or with disease recurrence occurring after 12 months of completing adjuvant endocrine therapy (with or without CDK4/6 inhibitors)
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.
• Adequate hematologic, hepatic, and renal functions.
• Female participants can be pre-, peri- or postmenopausal.
• Male and pre- or peri-menopausal female participants must be willing to take a GnRH (or LHRH) agonist.

Exclusion Criteria

• Disease recurrence during adjuvant endocrine therapy
• Currently receiving or previously received systemic anti-cancer therapy for ER+, HER2- advanced breast cancer.
• Previously received treatment with fulvestrant, elacestrant or an investigational endocrine therapy in any setting.
• History of allergic reactions to study treatment.
• Any contraindications to letrozole and ribociclib.
• Symptomatic central nervous system metastases, carcinomatous meningitis, leptomeningeal disease, or a spinal cord compression that require immediate treatment.