The p16 protein (also known as p16INK4a), encoded by the cyclin-dependent kinase inhibitor 2A (CDKN2A) gene, is a tumor suppressor, inhibiting cyclin-dependent kinases (CDK4/6) that maintain Rb in a phosphorylated state when bound to cyclin D1 (encoded by CCND1) [381,414,415]. The gene discussed is CCND1; the disease is neoplasm.