Cancer cells with elevated levels of cyclin D were highly sensitive to the CDK4/6 inhibition.42 We also found that the CDK4/6 inhibitor palbociclib displayed a similar profile while a less potency against ESCC cells compared to CYH33, further supporting the finding that intact G1/S transition rendered ESCC cells sensitive to CYH33. The gene discussed is CDK4; the disease is esophageal squamous cell carcinoma.