Three highly selective CDK4/6 inhibitors, palbociclib (PD-0332991), ribociclib (LEE001), and abemaciclib (LY2835219), have been recently approved by the FDA for treating ER+/HER2− advanced breast cancers, which are often characterized by dysregulated CDK4/6 activation15–19. The gene discussed is ESR1; the disease is breast carcinoma.