CCNA2 encodes cyclin A2, a regulatory protein controlling G1/S and G2/M cell cycle transitions through formation of kinase complexes with CDK1 or CDK2, conferring substrate specificity to these holoenzyme complexes 1. CCNA2-CDK2 complexes phosphorylate key cell cycle substrates, including the AXIN1 complex in lung cancer 2, and coordinate with transcriptional regulators like MYC to promote cell proliferation 3. Disease relevance is substantial: CCNA2 overexpression associates with poor prognosis across multiple cancers. In triple-negative breast cancer, elevated CCNA2 correlates with reduced disease-free survival 4. Similarly, in gastric cancer and breast cancer, CCNA2 upregulation predicts worse overall survival outcomes 51. In hepatocellular carcinoma, CCNA2 inhibition suppresses proliferation, migration, and epithelial-mesenchymal transition 6. Notably, smoking-induced CCNA2 overexpression in lung adenocarcinoma promotes alveolar type 2 cell differentiation into cancer stem cells through WNT/β-catenin pathway inactivation 2. In sepsis, paradoxically, reduced CCNA2 expression associates with improved 28-day survival 7. CCNA2 represents a promising therapeutic target and biomarker across solid malignancies.