Abemaciclib is a potent antiproliferative agent against HR+/HER2− breast cancer cells by selectively inhibiting CDK4/6‐mediated phosphorylation of retinoblastoma protein (RB), halting the cell cycle progression from G1 phase to S phase, and suppressing tumor cell proliferation.22, 23. The gene discussed is CDK4; the disease is breast carcinoma.