To determine if intrinsic levels of CIN may contribute to CDK4/6i efficacy, we assessed whether the effectiveness of CDK4/6i [palbociclib (14) and abemaciclib (39)] in breast cancer cell lines may be associated with their extent of aneuploidy [obtained from the broad Dependency Map (DepMap) project (40)]. The gene discussed is CDK4; the disease is breast cancer.