Leisure-time physical activity and breast cancer risk defined by estrogen and progesterone receptor status-The Japan Public Health Center-based Prospective Study

Objective. The study aims to investigate the association between leisure-time physical activity and breast cancer risk in consideration of tumor estrogen-receptor/progesterone-receptor status. Methods. We conducted a population-based prospective cohort study among 53,578 women in the Japan Public Health Center-based Prospective Study. Leisure-time physical activity was assessed by self-reported questionnaires. A Cox proportional hazards regression model was used to derive relative risks and 95% confidence intervals. Results. From 1990-1993 to the end of 2007, 652 cases were identified. The breast cancer rates (per 100,000 person-years) in the sedentary groups (<= 3 days/month) was 84 in overall, 97 in premenopausal and 75 in postmenopausal women. We observed a statistically significant inverse association between leisure-time physical activity and breast cancer risk (relative risk(>= 3) (days/week vs. <= 3 days/month) = 0.73; 95% confidence interval 0.54-1.00; p(trend) 0.037), particularly in estrogen receptor+progesterone receptor+ (relative risk 0.43; 0.19-1.00; p(trend) 0.022), and this inverse trend was apparent among postmenopausal women (relative risk 0.25; 0.06-1.06; p(trend) 0.041). An inverse trend was also observed between daily total physical activity and postmenopausal estrogen receptor + progesterone receptor + risk (p = 0.046). Among body mass index >= 25 kg/m(2) group, leisure-time physical activity was associated with decreased risk (relative risk(>= 1) (day/week vs. <= 3 days/month) = 0.65; 0.43-0.97; p(trend) 0.033). Conclusion. Active participation in leisure-time physical activity may contribute to a decrease in breast cancer risk, particularly for postmenopausal estrogen receptor + progesterone receptor + tumors. (C) 2011 Elsevier Inc. All rights reserved.