Do insulin-like growth factors mediate the effect of alcohol on breast cancer risk?

Despite a large number of epidemiologic studies demonstrating an increased risk of breast cancer in association with alcohol consumption, a causal relationship between alcohol intake and breast cancer risk remains to be determined. Several biological mechanisms have been proposed, but none of them explains well the features of the association, i.e. a modest increase in risk, a limited range of dose-response relationship and no further increase in risk among heavy drinkers. A new mechanism underlying a possible biological role of alcohol in breast cancer is proposed in this paper. Moderate consumption of alcohol increases the production of insulin-like growth factors (IGFs) by the liver and elevated IGFs via circulation stimulate or promote the development and/or growth of breast cancer. The effect of alcohol on IGF production declines among heavy drinkers as alcohol-caused liver-function damage results in no further increase in IGF production. Therefore, compared to moderate drinkers, heavy alcohol users do not have a higher risk of breast cancer.