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MONARCH 2: Abemaciclib/Fulvestrant in Hormone Receptor–Positive, HER2-Negative Breast Cancer

By: Cordi Craig
Posted: Monday, July 24, 2017

In the MONARCH 2 trial, conducted by George W. Sledge, Jr, MD, of Stanford University School of Medicine, and colleagues, the addition of abemaciclib, a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor, to the hormonal therapy fulvestrant improved outcomes in women with hormone receptor–positive, HER2-negative advanced breast cancer whose disease progressed while they were receiving endocrine therapy. These findings were reported at the 2017 American Society of Clinical Oncology (ASCO) Annual Meeting and published in the Journal of Clinical Oncology.

This phase III double-blind study was conducted at 142 sites in 19 countries between August 2014 and December 2015. A total of 669 patients were randomized to receive either the abemaciclib/fulvestrant combination (n=446) or placebo/fulvestrant (n=223).

At a median follow-up of 19.4 months, there were significant differences between the two groups, with median progression-free survival of 16.4 months in the abemaciclib plus fulvestrant group vs 9.3 months in the fulvestrant plus placebo group (P<.001). The objective response rate was 35% in the abemaciclib/fulvestrant group vs 16% in the placebo/fulvestrant group (P<.001). Adverse events, including diarrhea, neutropenia, nausea, and fatigue, were more common with abemaciclib.

The investigators concluded: “Abemaciclib at 150 mg twice daily plus fulvestrant was effective, significantly improving [progression-free survival] and [objective response rate] and demonstrating a tolerable safety profile in women with hormone receptor–positive HER2-negative [advanced breast cancer] who progressed while receiving [endocrine therapy].”