Since excessive proliferation of hepatocytes is a hallmark of HCC development [26], we then detected the main proliferation markers, PCNA, Ki67 and Cyclin B, in the liver tissues 10-month post DEN challenge and found that all those proliferation markers significantly decreased in DJ-1 KO mice compared with WT mice (Figure 2E). The gene discussed is PCNA; the disease is hepatocellular carcinoma.