Among postmenopausal women with hormone receptor (HR)-positive, HER2-negative breast cancer, treatment with abemaciclib, a potent, oral small-molecule inhibitor of CDK4 and 6, reduced Ki67 levels more than anastrozole, according to a study presented at the European Society for Medical Oncology (ESMO) 2016 Congress.1

Abemaciclib has demonstrated single-agent tumor activity and an acceptable safety profile when used in combination with an aromatase inhibitor. Researchers therefore evaluated the biological effects, activity, and safety of neoadjuvant abemaciclib plus anastrozole compared with abemaciclib monotherapy and anastrozole therapy in this breast cancer subpopulation.

For the open-label, phase neoMONARCH study ( Identifier: NCT02441946), researchers enrolled 173 patients with previously untreated early-stage breast cancer.

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Participants were randomly assigned 1:1:1 to receive abemaciclib plus anastrozole, abemaciclib monotherapy, or anastrozole monotherapy for the first 2 weeks. All patients received combination therapy during the subsequent 14 weeks. Patients also received diarrheal prophylaxis with loperamide prior with each dose of abemaciclib.

Results of a pre-specified 9-month interim analysis showed that combination therapy and abemaciclib were associated with a significantly greater reduction in Ki67 from baseline compared with anastrozole monotherapy.

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Researchers observed a greater number of Ki67 responses in the combination and abemaciclib monotherapy arms versus the anastrozole only arm.

Although any grade diarrhea and constipation were more common with the combination and abemaciclib, diarrhea was less frequent and less severe due to prophylactic treatment.                                 


  1. Hurvitz S, Abad M, Rostorfer R, et al. Interim results from neoMONARCH: A neoadjuvant phase II study of abemaciclib in postmenopausal women with HR +/ HER2- breast cancer (BC). Paper presented at: European Society for Medical Oncology (ESMO) 2016 Congress; October 7-11, 2016; Copenhagen, Denmark.