CCNA1 and hepatocellular carcinoma: The abnormal methylation of CCNA1 gene, especially in the CpG islands of gene promoter, could block the transcription, thus affecting the expression of CCNA1, which may lead to CCNA1 dysfunctions in cell differentiation and cell growth, contributing to the progression of many human tumors, such as HNSCC, NSCLC, CC, NPC, BCa, and HCC [9, 10, 20, 33–35].