Investigation of an interaction of alcohol intake and family history on breast cancer risk in the Minnesota breast cancer family study

BACKGROUND. One explanation for the variability in results in studies of al cohol consumption and breast cancer could be the presence of effect modifie rs, such as genetic susceptibility. The authors examined the interaction of alcohol and family history of breast cancer on breast cancer risk in a pop ulation-based family study of 426 multigenerational breast cancer families. The authors evaluated whether alcohol use was a stronger risk factor for b reast cancer among sisters, daughters, nieces, and granddaughters of breast cancer probands than among women who married into these families. METHODS. Analyses were performed on surrogate and self-reported data combin ed and on self-reported data alone. To evaluate the interaction of alcohol and breast cancer risk among women with a family history of breast cancer, the authors performed analyses on all 426 families and on a subset of 132 f amilies that had 3 or more breast and/or ovarian cancers in their family. RESULTS, A total of 9032 blood relatives and marry-ins and 558 breast cance r cases were available for analysis. In the entire 426 families, there was a suggestion of an interaction of relationship to the proband and frequency of alcohol consumption on breast cancer risk (P-interaction = 0.14) for su rrogate and self-reported information combined. Among first-degree relative s of the proband, daily drinkers had a significantly increased risk of brea st cancer compared with never drinkers (RR = 2.45 [1.20, 5.02]), but this i ncrease was less evident among second-degree relatives who reported daily a lcohol intake (RR = 1.27 [0.73, 2.22]) and was not evident in marry-ins who reported daily use of alcohol (RR = 0.90 [0.42, 1.90]). The findings based on the subset of 132 high-risk families with 3 or more breast and/or ovari an cancers were similar to findings based on all 426 families (P-interactio n = 0.07). An interaction of family history with alcohol use was also sugge sted when the analyses were restricted to self-respondents, although the in teraction test P-value was no longer of borderline significance. CONCLUSION. An increased risk of breast cancer due to an increased frequenc y of alcohol consumption may be limited to women with a family history of b reast cancer. (C) 2001 American Cancer Society.