Furthermore, certain cell cycle–related proteins, including TOP2A, PCNA, MCM2, MCM4, MCM5, MCM6, and MCM7, have also been reported (69–71) to facilitate cancer cell proliferation, and the enhanced expression of these cell cycle–related proteins may contribute to uncontrolled ESCC cell proliferation. The gene discussed is PCNA; the disease is esophageal squamous cell carcinoma.