As described in more detail in the accompanying article “Alcohol Metabolism and Cancer Risk,” there are seven types of ADH that are encoded by different genes. Moreover, two of the seven ADH genes, called ADH1B and ADH1C, are polymorphic—that is, they exist in more than one variant (i.e., allele). The enzymes encoded by these alleles differ in their activity and therefore result in the accumulation of different quantities of acetaldehyde. In Caucasians, polymorphism of the ADH1C gene is particularly relevant to cancer risk. This gene has two known alleles: a highly active allele called ADH1C*1 and a less active allele called ADH1C*2. Several case–control studies1 have assessed the relationship between the active ADH1C*1 allele (and, thus, elevated acetaldehyde levels) and the risk of breast cancer. Of these, three studies concluded that the ADH1C*1 allele plays a role in breast cancer development, particularly in women who have not yet entered menopause (i.e., are premenopausal); conversely, one study did not find such a positive correlation.
