Palbociclib (Ibrance®) (8) [237,238], ribociclib (Kisqali®) (Ribotix®) (9) [239,240,241], and abemaciclib (Verzenio®) (10) [242] are FDA-approved CDK4/CDK6 inhibitors that are used therapeutically for breast cancer [37,243]. This evidence concerns the gene CDK4 and breast cancer.