Abemaciclib, sold under the brand name Verzenio among others, is a medication for the treatment of advanced or metastatic breast cancers.

[4] It was designated as a breakthrough therapy for breast cancer by the US Food and Drug Administration (FDA) in October 2015.

[8] These enzymes are responsible for phosphorylating and thus deactivating the retinoblastoma protein, which plays a role in cell cycle progression from the G1 (first gap) to the S (synthesis) phase.

The substance is mainly metabolized by the liver enzyme CYP3A4 to N-desethylabemaciclib (M2), and to a lesser extent to hydroxy derivatives (M18, M20) and another oxidative metabolite (M1).

[13] Abemaciclib was approved by the FDA in September 2017 either in combination with fulvestrant or as a monotherapy for women with HR+, HER2- advanced or metastatic breast cancer that had progressed while receiving endocrine therapy.