Site Editor

William J. Gradishar, MD, FACP, FASCO


Advanced Breast Cancer: Is Abemaciclib Plus Endocrine Therapy of Benefit After Disease Progression?

By: Justine Landin, PhD
Posted: Friday, June 21, 2024

Researchers from multiple institutes investigated the impact of abemaciclib plus fulvestrant compared with fulvestrant alone for the treatment of hormone-receptor (HR)-positive, HER2-negative breast cancer. The addition of this CDK4/6 inhibitor to endocrine therapy improved clinical outcomes for patients whose disease had previously progressed after endocrine therapy and CDK4/6 inhibition. These primary outcomes from the phase III postMONARCH trial were presented by Kevin Kalinsky, MD, MS, of Winship Cancer Institute of Emory University, Atlanta, and colleagues at the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting (Abstract LBA1001).

“Abemaciclib plus fulvestrant demonstrated statistically significant progression-free survival improvement in patients with advanced breast cancer progression on prior CDK4/6 inhibitor-containing therapy. Consistent effect was seen across major clinical and genomic subgroups, including patients with baseline ESR1 or PIK3CA mutations,” stated the investigators.

This global, double-blind, placebo-controlled study included patients with advanced breast cancer (n = 368) who experienced disease progression with CDK4/6 and aromatase inhibition as initial therapy or who relapsed during or after adjuvant therapy with CDK4/6 inhibition and endocrine therapy. Patients who had undergone any other treatments for advanced breast cancer were not included in the study. Prior CDK4/6 inhibition included the use of palbociclib (59%), ribociclib, (33%), and abemaciclib (8%). Patients were randomly assigned to receive fulvestrant with abemaciclib (n = 182) or placebo (n = 186).

At interim analysis, prespecified criteria for improved investigator-assessed progression-free survival was reached with the addition of abemaciclib to fulvestrant (169 events, hazard ratio [HR] = 0.66, 95% confidence interval [CI] = 0.48–0.91, P = .01). At primary analysis, the 6-month progression-free survival rate was 50% with abemaciblib plus fulvestrant vs 37% with fulvestrant alone (258 events, HR = 0.73, 95% CI = 0.57–0.95). The objective response rate was also improved with the addition of abemaciblib (17%) vs fulvestrant alone (7%), and overall survival data remain immature (20.9% event rate). No new safety signals with the use of abemaciclib were observed.

Disclosure: For full disclosures of the study authors, visit

By continuing to browse this site you permit us and our partners to place identification cookies on your browser and agree to our use of cookies to identify you for marketing. Read our Privacy Policy to learn more.