Alcohol Consumption, Cigarette Smoking, and Risk of Breast Cancer for and Mutation Carriers: Results from The BRCA1 and BRCA2 Cohort Consortium.

Background: Tobacco smoking and alcohol consumption have been intensively studied in the general population to assess their effects on the risk of breast cancer, but very few studies have examined these effects in and mutation carriers. Given the high breast cancer risk for mutation carriers and the importance of and in DNA repair, better evidence on the associations of these lifestyle factors with breast cancer risk is essential.

Methods: Using a large international pooled cohort of and mutation carriers, we conducted retrospective (5,707 mutation carriers and 3,525 mutation carriers) and prospective (2,276 mutation carriers and 1,610 mutation carriers) analyses of alcohol and tobacco consumption using Cox proportional hazards models.

Results: For both and mutation carriers, none of the smoking-related variables was associated with breast cancer risk, except smoking for more than 5 years before a first full-term pregnancy (FFTP) when compared with parous women who never smoked. For mutation carriers, the HR from retrospective analysis (HR) was 1.19 [95% confidence interval (CI), 1.02-1.39] and the HR from prospective analysis (HR) was 1.36 (95% CI, 0.99-1.87). For mutation carriers, smoking for more than 5 years before an FFTP showed an association of a similar magnitude, but the confidence limits were wider (HR = 1.25; 95% CI, 1.01-1.55 and HR = 1.30; 95% CI, 0.83-2.01). For both carrier groups, alcohol consumption was not associated with breast cancer risk.

Conclusions: The finding that smoking during the prereproductive years increases breast cancer risk for mutation carriers warrants further investigation.

Impact: This is the largest prospective study of mutation carriers to assess these important risk factors.