Our analysis focused on the four major human alcohol metabolism genes or gene clusters, including ADH, CYP2E1, ALDH1, and ALDH2. Variants in these genes have been previously investigated for influencing ethanol metabolism or modifying the effect of alcohol on breast cancer risk, including ADH1B*2 (rs1229984), ADH1B*3 (rs2066702), ADH1C*1 (rs698), CYP2E1*5 (rs2031920-T, rs3813867-C, and rs6413432-A), CYP2E1*6 (rs6413432-A) and ALDH2*2 (rs671) [53, 57]. The gene discussed is ALDH2; the disease is breast cancer.