CCNE2 encodes cyclin E2, a regulatory protein essential for cell cycle control at the G1/S transition 1. The protein functions by forming a complex with CDK2 to phosphorylate specific substrates that promote DNA replication and cell cycle progression 1. CCNE2 is subject to post-translational modifications including lactylation, which promotes hepatocellular carcinoma (HCC) cell growth, while SIRT3-mediated delactylation suppresses HCC development 2. The protein plays significant roles in cancer biology, with oncogenic activation leading to replication stress and genomic instability 1. CCNE2 overexpression contributes to trastuzumab resistance in HER2+ breast cancer, where miR-26a and miR-30b normally regulate its expression 3. Additionally, CCNE2 alterations confer resistance to CDK4/6 inhibitors in hormone receptor-positive breast cancer 4. The gene is also transcriptionally suppressed by E2F2 degradation pathways 5 and represents a potential therapeutic target in visceral adipose tissue for type 2 diabetes 6. These findings highlight CCNE2's dual role in normal cell cycle regulation and cancer pathogenesis, making it a clinically relevant target for therapeutic intervention.