Alcohol and postmenopausal breast cancer risk defined by estrogen and progesterone receptor status: A prospective cohort study

Background: Alcohol intake has been reported to be positively associated with an increased risk of postmenopausal breast cancer; however, the association with the estrogen receptor (ER) and progesterone receptor (PR) status of the breast tumors remains unclear. Methods: Self-reported data on alcohol consumption were collected in 1987 and 1997 from 51847 postmenopausal women in the population-based Swedish Mammography Cohort. Through June 30, 2004, 1188 invasive breast cancer case patients with known ER and PR status were identified during an average 8.3-year follow-up. We used Cox proportional hazards models to estimate multivariable relative risks (RRs) of breast cancer, adjusting for age; family history of breast cancer; body mass index; height; parity; age at menarche, first birth, and menopause; education level; use of postmenopausal hormones; and diet. Heterogeneity among groups was evaluated using the Wald test. All statistical tests were two-sided. Results: Alcohol consumption was associated with an increased risk for the development of ER-positive (+) tumors, irrespective of PR status (highest intake [≥10 g of alcohol per day] versus nondrinkers, multivariable RR = 1.35, 95% confidence interval [CI] = 1.02 to 1.80; P_trend<.049 for ER+PR+ tumors; and RR = 2.36, 95% CI + 1.56 to 3.56; P_trend<.001 for ER+PR- tumors). The absolute rate of ER+ breast cancer (standardized to the age distribution of person-years experienced by all study participants using 5-year age categories) was 232 per 100000 person-years among women in the highest category of alcohol intake, and 158 per 100000 person-years among nondrinkers. No association was observed between alcohol intake and the risk of developing ER- tumors. Furthermore, we observed a statistically significant interaction between alcohol intake and the use of postmenopausal hormones on the risk for ER+PR+ tumors (P_interaction = .039). Conclusion: The observed association between risk of developing postmenopausal ER+ breast cancer and alcohol drinking, especially among those women who use postmenopausal hormones, may be important, because the majority of breast tumors among postmenopausal women overexpress ER.