Alcohol consumption and breast cancer risk among postmenopausal women following the cessation of hormone therapy use: The California Teachers Study

Background: Alcohol consumption increases breast cancer risk, but its effect may be modified by hormone therapy (HT) use, such that exposure to bothmaybe synergistic. Because manywomenstopped taking HT after mid-2002, it is important to quantify risks associated with alcohol consumption in the context of HT cessation, as these risks may be more relevant to cancer prevention efforts today. Methods: Among 40,680 eligible postmenopausal California Teachers Study cohort participants, 660 were diagnosed with invasive breast cancer before 2010. Multivariate Cox proportional hazards regression models were used to estimate relative risks (RR) and 95% confidence intervals (CI). Results: Increased breast cancer risk associated with alcohol consumption was observed among postmenopausal women who were current HT users [RR, 1.60; 95% confidence interval (CI), 1.13-2.26 and RR, 2.11; 95% CI, 1.41-3.15 for <20 and ≥20 g/d of alcohol], with risks being similar by HT preparation. Alcohol did not increase risk among women who had stopped using HT within 3 years or 3 to 4 years before completing the follow-up questionnaire or in the more distant past. Results were similar for estrogen receptor positive (ER+) and ER+PR+ progesterone receptors positive (PR+) tumors; while power was limited, no increase in risk was observed for ER- tumors. Conclusions: Following the cessation of HT use, alcohol consumption is not significantly associated with breast cancer risk, although a nonsignificant increased risk was observed among women who never used HT. Impact: Our findings confirm that concurrent exposure to HT and alcohol has a substantial adverse impact on breast cancer risk. However, after HT cessation, this risk is reduced.