Palbociclib, the specific inhibitor for cyclin-dependent kinase 4/6 (CDK4/6), emerged as a promising therapeutic agent to treat various cancers.[5,6] Palbociclib inhibits cell proliferation by blocking the kinase activity of the cyclin D–CDK4/6 complex, resulting in hypophosphorylation of retinoblastoma (Rb), and subsequently, deactivation of the E2F transcription factor that leads to cell cycle arrest at the G1 phase (Fig. 1). The gene discussed is CDK4; the disease is cancer.