Abemaciclib Plus Nonsteroidal Aromatase Inhibitor Improved Survival Outcomes Among Patients With HR-Positive, HER2-Negative Advanced Breast Cancer

According to final overall survival (OS) results from the MONARCH 3 study, abemaciclib plus a nonsteroidal aromatase inhibitor (NSAI) improved OS and prolonged progression-free survival (PFS) among patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer. 

As previously reported, results demonstrated a “significantly prolonged PFS with the addition of abemaciclib versus placebo to NSAI…[and] at the last interim OS analysis, a numerically favorable median OS difference of 12.6 months was observed,” stated Matthew Goetz, MD, Mayo Clinic, Rochester, Minnesota, and coauthors. “Here, we present the prespecified final OS results.” 

This double-blind, placebo-controlled study enrolled 493 postmenopausal patients with HR-positive, HER2-negative advanced breast cancer, who did not receive systemic therapy in the advanced setting. Patients were randomized on a 2-to-1 basis to receive either 150 mg of abemaciclib (n = 328) or placebo (n = 165) plus physician’s choice anastrozole (1 mg) or letrozole (2.5 mg) in 28-day cycles. The primary end point was investigator-assessed PFS. A key secondary end point was OS. Chemotherapy-free survival (CFS) was an exploratory end point. 

After a median follow-up of 8.1 years, median PFS was 29 months in the abemaciclib arm and 14.8 months in the placebo arm. At that time, 198 OS events occurred in the abemaciclib arm and 116 OS events occurred in the placebo arm (hazard ratio [HR], 0.804; 95% confidence interval [CI], 0.637 to 1.015; P = .0664). Median OS was 66.8 months in the abemaciclib arm and 53.7 months in the placebo arm. Median CFS was 46.7 months in the abemaciclib arm and 30.6 months in the placebo arm (HR, 0.693; 95% CI, 0.557 to 0.863; P = .0010). 

“These data continue to support the consistent and meaningful clinical benefit abemaciclib has demonstrated across the MONARCH program,” concluded Dr Goetz et al.

Source: 

Goetz MP, Toi M, Huober J, et al. Abemaciclib plus a nonsteroidal aromatase inhibitor as initial therapy for HR+, HER2- advanced breast cancer: Final overall survival results of MONARCH 3. Ann Oncol. Published online: May 8, 2024. doi: 10.1016/j.annonc.2024.04.013