This might infer that O. viverrine infection might potentially increase the risk of CCA, but its carcinogenesis impact in the general population might not be as high as in the population in Northeastern Thailand, which might be regional-unique from both biological and environmental factors, including exposure to toxins in some local foods, for example, fermented meat and nitrate containing foods [3, 13, 14], high parasite load, as well as genetically susceptible to noxious effect from O. viverrini infection, for example, GSTM1 [13, 14] or MTHFR polymorphisms [15]. This evidence concerns the gene GSTM1 and cholangiocarcinoma.