MTRR and cancer: While there was no clear overall association between SNPs in MTR and MTRR and any cancer in main effect analyses (Table 2), heterogeneity of association was suggested in stratified analyses on alcohol consumption, including associations of MTR rs1805087 with liver cancer (homogeneity P = 0.021), and MTRR rs1801394 with both esophageal (homogeneity P = 0.005) and stomach cancer (homogeneity P = 0.004).