Multinational phase 3 trial of abemaciclib plus fulvestrant for HR-positive, HER2-negative advanced breast cancer: final OS results from MONARCH 2

De multinational phase 3 MONARCH 2 trial randomized CDK4/6-naïve patients with HR-positive, HER2-negative advanced breast cancer and progression on endocrine therapy 2:1 to abemaciclib plus fulvestrant or placebo plus fulvestrant. Ten-year follow-up of the trial showed that progression-free survival, overall survival, and chemotherapy-free survival were better with abemaciclib compared with placebo. The OS benefit with abemaciclib was numerically greater in subgroups with worse prognosis, such as visceral disease, primary resistance to endocrine therapy, and PR-negative status. No new safety signals or cumulative toxicities were identified. The authors conclude that addition of abemaciclib to fulvestrant was associated with improved outcomes in this patient population.