Monarch 2: Abemaciclib In Combination With Fulvestrant In Patients With Hr+/Her2-Advanced Breast Cancer Who Progressed On Endocrine Therapy

1000Background: Abemaciclib, an oral, selective inhibitor of CDK4 u0026 6, dosed on a continuous schedule, demonstrated clinical activity as monotherapy in patients (pts) with treatment refractory hormone receptor positive (HR+) metastatic breast cancer (MBC). The tolerability and activity of abemaciclib + fulvestrant (F) supported Phase 3 evaluation. Methods: MONARCH 2 is a double-blind Phase 3 trial of abemaciclib + F vs placebo (P) + F in women with HR+/HER2- advanced breast cancer. Women who progressed on (neo)adjuvant endocrine therapy (ET), ≤12 months from end of adjuvant ET, or on first line ET for MBC and who had not received chemotherapy for metastatic disease were eligible. Pts were randomized 2:1 to receive abemaciclib at 150 mg Q12H (or 200 mg prior to amendment) or P plus F (500 mg, per label) and stratified by metastatic site (visceral, bone only, or other) and resistance to prior ET (primary vs secondary). Pre/perimenopausal pts received a gonadotropin-releasing hormone agonist. The primary obj...