Neoadjuvant therapy with the investigational oral CDK 4/6 inhibitor abemaciclib as monotherapy and with anastrozole reduced Ki67 levels more than anastrozole monotherapy in postmenopausal patients’ early-stage, hormone receptor (HR)-positive, HER2-negative breast cancer cells, according to early findings presented at the 2016 San Antonio Breast Cancer Symposium.1

“We found that abemaciclib reduced levels of Ki67 in HR-positive, HER2-negative breast cancer cells,” said Sara A. Hurvitz, MD, of the Jonsson Comprehensive Cancer Center in Los Angeles, California. “More definitive clinical evaluation of these therapeutics in the early-stage setting should be a priority.”

No new safety signals were identified for continuous abemaciclib 150mg dosing, Dr Hurvitz cautioned.

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Therapy durations were short, precluding “robust assessment” of pathologic responses, she cautioned.

But the majority of patients administered abemaciclib and anastrozole saw objective responses and abemaciclib induced “profound cell cycle arrest, defined by decreased Ki67 and E2F targeted proliferation mRNAs,” she said.

Ki67 levels are indicative of impaired cell proliferation and have been previously correlated with improved outcomes, indicating that CDK 4/6 inhibitors like abemaciclib might be promising therapeutics for early-stage cancers, Dr Hurvitz said.

The research team randomly assigned 223 women with early-stage breast cancer to receive neoadjuvant therapy with anastrozole, abemaciclib, or both, for 2 weeks. Participants subsequently received anastrozole and abemaciclib (150mg) for 14 more weeks prior to surgery.

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Core biopsies were taken at baseline and after the first 2 weeks of treatment for Ki67 analysis. Abemaciclib-associated Ki67 suppression was significantly greater than anastrozole (-90.6 vs -63.2 geometric mean change [P < 0.001]).

“These data support continued evaluation of abemaciclib in patients with early-stage breast cancer,” Dr Hurvitz concluded.


  1. Hurvitz S, Martin M, Fernandez Abad M, et al. Biological effects of abemaciclib in a phase 2 neoadjuvant study for postmenopausal patients with HR+, HER2- breast cancer. Paper presented at: 39th San Antonio Breast Cancer Symposium; Dec 2016; San Antonio, TX.