CDKN2D (Cyclin-Dependent Kinase Inhibitor 2D): CDKN2D is a member of the INK4 family of cyclin-dependent kinase inhibitors. It plays a key role in regulating cell cycle progression by inhibiting CDK4 and CDK6. This inhibition prevents phosphorylation of the retinoblastoma protein, causing cell cycle arrest in the G1 phase. CDKN2D functions as a tumor suppressor, making it essential for controlling cell proliferation, and its loss has been linked to the development of various cancers.