Abstract
The prevalence of binge drinking in the United States is rising. While alcohol is a risk factor for breast cancer, less is known about the impact of episodic heavy drinking. In 2003-2009, women aged 35-74 years who were free of breast cancer were enrolled in the Sister Study (n = 50,884). Residents of the United States or Puerto Rico who had a sister with breast cancer were eligible. Multivariable Cox regression was used to estimate adjusted hazard ratios and 95% confidence intervals for breast cancer. During follow-up (mean = 6.4 years), 1,843 invasive breast cancers were diagnosed. Increased breast cancer risk was observed for higher lifetime alcohol intake (for ≥230 drinks/year vs. <60 drinks/year, hazard ratio (HR) = 1.35, 95% confidence interval (CI): 1.15, 1.58). Relative to low-level drinkers (<60 drinks/year), hazard ratios were increased for ever binge drinking (HR = 1.29, 95% CI: 1.15, 1.45) or blacking out (HR = 1.39, 95% CI: 1.17, 1.64). Compared with low-level drinkers who never binged, moderate drinkers (60-229 drinks/year) who binged had a higher risk (HR = 1.25, 95% CI: 1.08, 1.44). There was evidence of effect modification between moderate lifetime drinking and binging (relative excess risk due to interaction = 0.33, 95% CI: 0.10, 0.57). Our findings support the established association between lifetime alcohol intake and breast cancer and provide evidence for an increased risk associated with heavy episodic drinking, especially among moderate lifetime drinkers.