GSTP1 and hepatocellular carcinoma: Another study investigated the methylation levels of GSTP1, RASSF1A, APC, and SFRP1 genes in the plasma of 72 HCC patients and 37 people with benign liver diseases, and showed that methylation level of RASSF1A was correlated with the tumor size; methylation level of GSTP was correlated with an increase in serum AFP concentrations, while hypermethylation of SFRP1 was more frequent in women [24].