Body Size and Risk for Breast Cancer in Relation to Estrogen and Progesterone Receptor Status in Japan

Purpose The aim of this study is to examine the association of height, weight, and body mass index (BMI) with breast cancer and its hormone receptor–defined subtype in a low-risk population. Methods We identified 441 newly diagnosed cases of breast cancer during a 9.9-year follow-up of a population-based cohort consisting of 55,537 women aged 40 to 69 years. Body size was assessed by using a self-administered questionnaire. Results We found a significant positive association of height and marginally significant positive associations of weight and BMI with breast cancer in postmenopausal women. Weight and BMI were associated more strongly with estrogen receptor–positive (ER+) than ER-negative (ER−) breast cancer in postmenopausal women. BMI was related significantly to increased risk for ER+ (hazard ratio [HR] per BMI increment of 1 kg/m2, 1.08; 95% confidence interval [CI], 1.01–1.15), but not ER− breast cancer (HR per BMI increment of 1 kg/m2, 0.95; 95% CI, 0.84–1.06; p for difference of HRs = 0.048). Conclusions The present study suggests that height, weight, and BMI are associated with increased risk for breast cancer among postmenopausal women in Japan. The positive association of weight and BMI might be limited to ER+ breast cancer.