SMAD6 and neoplasm: We found that 7 genes (IFITM1, SMAD6, TBX15, CHST4, LRRC4, CCL20, and NQO1) showed significantly different promoter methylation levels between tumor and non-tumor tissue (P value < 0.001) in approximately 80 % of the 78 HCCs (Fig. 2a).