The Human Protein Atlas (HPA) results showed that the CDK4 gene was highly expressed in liver cancer tissues, the CDK1, SRC, and CDK2 genes were moderately expressed in liver cancer tissues, and the PCNA, and RB1 genes were lowly expressed in liver cancer tissues, but not expressed in normal liver tissues, the CCND1 gene was highly expressed in liver cancer tissues and normal liver tissues. The gene discussed is PCNA; the disease is liver cancer.