One of the risk factors for breast cancer is an increased blood level of female sex hormones (i.e., estrogens), the most important of which is called estradiol. In some cases of breast cancer, the cancer cells carry docking molecules (i.e., receptors) for estrogens on their surface; these cancer cells depend on estrogen to grow. In other breast cancer cases, however, no estrogen receptors are found and these cells grow even without estrogen. Alcohol consumption and alcohol metabolism by ADH appear to affect the levels of estrogen and estrogen receptors, which may contribute to the alcohol–breast cancer association. However, this issue still needs to be fully elucidated. What currently is known is the following: The enzyme encoded by ADH1C not only metabolizes alcohol to acetaldehyde but also is involved in the metabolism of steroid hormones, including estrogens (McEvily et al. 1988).Some evidence suggests that alcohol enhances the expression of estrogen receptors in breast cells (Fan et al. 2000), which would increase breast cancer risk.Both in women with a normal menstrual cycle and in women taking oral contraceptives, blood concentrations of acetaldehyde
