An important question in this context is the expression of ALDH2 in the human breast, which would be protective against acetaldehyde generated from local alcohol metabolism. Publicly available datasets (http://www.nih.gov/geo) indicate low levels of ALDH2 mRNA expression in human mammary gland, but to our knowledge there is no published evidence of ALDH2 enzymatic activity in this tissue. If ALDH2 enzyme is active in the human breast epithelial cells, women expressing the inactive form of ALDH2 could be at elevated risk of breast cancer from alcohol drinking. One Japanese study (Kawase et al., 2009) did not observe this effect, but this study included only 11 such ALDH2-deficient individuals drinking more than 15 gm/day.
