While changes in sex hormones in relation to alcohol consumption have received the most attention in the epidemiology literature, moderate alcohol drinking may have other biological effects on an initiated tumor that could be of potential relevance to the observed breast cancer risk. The epithelial–mesenchymal transition (EMT) is emerging as an important mechanism in the development of invasive cancer (Kalluri and Weinberg, 2009). (Forsyth et al., 2010) recently found that ethanol stimulates the EMT in human breast cancer cells in vitro. Notably, the ethanol concentrations used in this work were consistent with those that could be attained during moderate drinking. If these in vitro results are applicable to human breast cancers in vivo, then ethanol stimulation of the EMT could provide a mechanistically and temporally plausible explanation for the observed relationship between moderate alcohol consumption on breast cancer risk. Similarly, a recent in vitro study showed that alcohol increased the invasiveness of human breast cancer cells (Wong et al., 2011b). Again, if the mechanisms described in this work are operative in vivo, they could provide clinical relevant targets for alcohol-related breast cancer.
