Alcohol and Breast Cancer
Authors: Marsha E. Reichman
Journal: New England Journal of Medicine (1987)

Little is known about the risk factors that predispose women to breast cancer. Moreover, a woman can do nothing to change most identified risk factors, such as family menstrual period. Mounting evidence suggests an association between breast cancer and alcohol consumption. Research is underway to clarify the nature of this association. If alcohol's role is causal, reducing alcohol consumption can be a potential means of lowering the risk of breast cancer. If alcohol is not a causal factor, research on the alcohol-breast cancer association nevertheless may increase knowledge of cancer development and the effects of alcohol on hormonal systems. Epidemiology of Alcohol and Breast Cancer The vast majority of studies on alcohol and breast cancer indicate a weak positive association, with relative risks in the range of 1.2 to 2,0. This means that the risk of developing breast cancer among groups of women consume alcohol is approximately 1.2 to 2.0 times the risk in groups who do not consume alcohol. Relative risks at the upper end of this spectrum (about 2.0) usually are observed among women who consume the equivalent of two or more drinks per day. The above generalization is derived from results of two types of epidemiologic research: followup studies and case-control studies. In followup studies, subjects are recruited at the beginning of the study. Data collected at this point (i.e., baseline information) are stored until endpoints of interest, such as occurrence of breast cancer, are determined. Associations are then examined between baseline information and subsequent development of disease. Case-control studies include subjects with recently diagnosed breast cancer along with one or more control groups of subjects who do not have breast cancer. The control subjects are usually matched to breast cancer subjects in terms of age and other characteristics. The matched characteristics can then be eliminated from consideration when comparing the groups to determine the factors (e.g., alcohol consumption) associated with the disease. In general, case-control studies are believed to be less reliable than followup studies because of potential problems associated with subject selection and with subjects' recall of information. Early research on alcohol consumption and breast cancer was reviewed by Longnecker and colleagues in 1988. This analysis included 4 followup studies and 12 case-control studies. The followup studies showed clear evidence of a significant association, whereas the case-control studies provided conflicting results. An analysis of all data from these studies demonstrated a dose-response effect, whereby increasing doses of alcohol were associated with increasing relative risk. The relative risk for breast cancer associated with consumption of 24 grams of alcohol (about two drinks) per day was 1.4 based on case-control data and 1.7 based on followup data. Longnecker and coworkers also concluded, based on available data, that 13 percent of all breast cancer cases in the United States might be attributable to alcohol consumption. More recent research was reviewed by Hiatt (1990) and Rosenberg and colleagues (1993). Six of nine followup studies published to date showed significantly elevated relative risks. Relative risks of breast cancer for alcohol consumption of fewer than two drinks per day were between 1.2 and 1.5. At higher levels (five drinks a day or more), relative risks were between 2.1 and 3.3. As for case-control studies (Hiatt 1990; Rosenberg et al. 1993), the relative risks associated with one drink per day were generally 1.4 or less. The relative risks associated with two or more drinks per day were originating in France and Italy had substantially higher relative risks than those from the United States. For alcohol consumption in excess of two drinks per day, French and Italian studies tend to show relative risks between 2.0 and 2.5. This may be a result of different drinking patterns, particularly for wine consumption, in these countries. …