Initial Therapy With Abemaciclib for Advanced Breast Cancer
Abemaciclib, a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor, in combination with a nonsteroidal aromatase inhibitor was shown to be effective in hormone receptor–positive, HER2-negative advanced breast cancer. The results of the MONARCH 3 study were published by Matthew Goetz, MD, of the Mayo Clinic in Rochester, Minnesota, and colleagues in the Journal of Clinical Oncology.
The double-blind, randomized phase III study included 493 postmenopausal women. Patients with hormone receptor–positive, HER-2 negative breast cancer who did not respond to previous endocrine therapy met the inclusion criteria. Those assigned to the treatment group received abemaciclib at 150 mg twice a day in combination with a daily dosed nonsteroidal aromatase inhibitor (anastrozole at 1.0 mg or letrozole at 2.5 mg) versus the nontreatment placebo group.
An investigator-assessed interim analysis was conducted after 194 progression-free survival events occurred. The median progression-free survival rate was significantly increased in the treatment group, with a hazard ratio of 0.54. The response rate was 59% in the treated group compared with 44% in the placebo group. The most frequent adverse events observed with abemaciclib were neutropenia, diarrhea, and leukopenia.