In the top 10 down-regulated genes, SPP2, LECT2, SLC10A1, CYP2A6, CYP3A4, HSD17B13, CYP2A7, and IYD expression were significantly down-regulated, while CYP7A1 expression was up-regulated in tumor tissues in comparison to normal liver tissues (Fig. 2b); notably, SPP2, LECT2, SLC10A1, CYP3A4, HSD17B13, and IYD predicted a better prognosis in HCC patients (Fig. 2c and Supplementary Fig. 1). The gene discussed is CYP2A6; the disease is hepatocellular carcinoma.