Alcohol and breast cancer: update from an Italian case-control study

The analysis of alcohol and breast cancer risk from an Italian case-control study of breast cancer has been updated to include a total of 2402 women with histologically confirmed breast cancer and 2220 controls with acute conditions unrelated to any of the established or potential risk factors for breast cancer, admitted to a network of teaching and general hospitals in the greater Milan area. Compared with non-drinkers, the estimated relative risk for ever drinkers was 1.4 (95% CI = 1.2-1.6). The multivariate risks were 1.3 for less than 1 drink (e.g. 10 g of ethanol) per day, 1.3 for 1 less than 2 drinks, 1.4 for 2-3 and 2.2 for over 3 drinks per day. The positive association between alcohol and breast cancer was consistent across strata of age, socio-demographic variables, smoking, menstrual, reproductive, and hormonal factors, family history of breast cancer, nutrition and diet indicators. In particular, this study indicated that the alcohol-breast cancer relationship is probably not materially different in younger and older women, that alcohol drinking at an early age is not a particularly clear indicator of subsequent risk, nor that the effect of alcohol is enhanced in thin women. Thus, the findings of this study are both internally consistent and in agreement with most previous evidence, since the relative risks of 1.3-1.4 for a consumption of 10-30 g of alcohol per day compare well with the corresponding highest intake levels in most American studies. This study is of particular interest, since it provides data on higher levels of alcohol consumption, on which very little information is available. There are nontheless at least three elements which leave open the question of causality: the absence of duration-risk relationship, the inconsistency with evidence from descriptive epidemiology, and the lack of plausible biological mechanisms.