The inactivation of p16INK4a, a CDK inhibitor that inactivates CDK4/6 and prevents cell cycle progression at the G1/S checkpoint, resulting in the loss of cell cycle control, while dysregulation of the CDK4/6-cyclin D1 complex is a crucial stage in the genesis of breast cancer [43–46]. The gene discussed is CDKN2A; the disease is breast cancer.