It has been reported in the PALOMA-2 trial that more than 30% patients experienced recurrence of their cancer within 2 years of CDK4/6 inhibitor treatment (Finn et al., 2016), indicating that palbociclib combined with endocrine therapy may affect CDK inhibitor sensitivity and allow tumor cells to return to a proliferative phenotype. The gene discussed is CDK4; the disease is neoplasm.