CCND2 (cyclin D2) is a regulatory component of the cyclin D2-CDK4 complex that controls G1/S phase transition in the cell cycle 1. As a key integrator of mitogenic signals, CCND2 phosphorylates retinoblastoma protein (RB1), enabling dissociation of E2F transcription factors and subsequent S-phase gene expression 1. During early G1 phase, CCND2 hypophosphorylates RB1 to enforce commitment to DNA replication 1. Beyond canonical cell-cycle control, CCND2 has emerged as functionally important in regenerative medicine and disease contexts. CCND2 overexpression in induced pluripotent stem cell-derived cardiomyocytes significantly enhanced myocardial repair following infarction in a swine model, improving left ventricular function and reducing fibrosis through enhanced cell proliferation and paracrine signaling 2. In pancreatic development, CCND2 plays a secondary role to CCNA2 in perinatal β-cell proliferation, with CCND2-antisense 1 lincRNA positively regulating cyclin D2 expression 3. CCND2 dysregulation contributes to malignancy. CCND2 translocations characterize cyclin D1-negative mantle cell lymphoma cases 4, and CCND2 amplification occurs in malignant gliomas 5. MicroRNA-610 suppresses glioblastoma proliferation by directly targeting CCND2 6. CCND2 promoter methylation correlates with hepatocellular carcinoma progression and combines with AFP for improved diagnostic sensitivity 7.