CCND1 encodes cyclin D1, a regulatory protein essential for cell cycle progression through the G1/S transition 123. Cyclin D1 functions as the regulatory component of the cyclin D1-CDK4 complex, which phosphorylates retinoblastoma (RB) protein family members, including RB1 14. This phosphorylation releases the transcription factor E2F from RB/E2F complexes, enabling transcription of E2F target genes that promote G1 phase progression 15. Cyclin D-CDK4 complexes integrate mitogenic and antimitogenic signals 3. Beyond cell cycle regulation, cyclin D1 exhibits transcriptional corepressor activity with INSM1 on NEUROD1 and INS promoters in a cell cycle-independent manner 6. Dysregulation of CCND1 is clinically significant in multiple malignancies. Mantle cell lymphoma is characterized by constitutive CCND1 overexpression through t(11;14)(CCND1;IGH) translocation 7. In gastric cancer, circNFATC3 enhances CCND1 mRNA stability through IGF2BP3 interaction, promoting cell proliferation 8. Multiple myeloma with t(11;14)(CCND1;IGH) shows venetoclax sensitivity, though resistance mechanisms involving RAS pathway mutations and genomic alterations emerge during treatment 9. Elevated CCND1 expression in chr11 hepatitis B-related liver fibrosis/cirrhosis correlates with immune infiltration patterns 10. The CCND1 c.870G>A polymorphism is associated with increased breast cancer risk in Caucasian populations 11 and brain tumor susceptibility, particularly gliomas 12.