Purpose: The associations between anthropometric factors, physical activity (PA), and breast cancer risk in terms of estrogen-receptor/progesterone-receptor (ER/PgR) status have been unclear in Japanese women. This case-control study was designed to evaluate these associations.
Methods: From among female patients aged 30 years and over admitted to a single hospital in Japan between 1997 and 2009, 1,017 breast cancer cases (538ER+/PgR+, 125ER+/PgR-, 23 ER-/PgR+, 249 ER-/PgR-, and 82 missing) and 2,902 controls were selected. Height, weight, body mass index (BMI) (kg/m(2)), and time spent exercising (hours/week) were assessed using a self-administered questionnaire. Polytomous logistic regression analysis and tests for heterogeneity across ER+/PgR+ and ER-/PgR- were conducted.
Results: Higher BMI was associated with a higher risk of ER+/PgR+ cancer among women overall [odds ratio (OR) = 2.41, 95 % confidence interval (CI) 1.37-4.23 for BMI ≥30.0; P(trend) = 0.0001] and postmenopausal women (OR = 6.24, 95 % CI 2.68-14.53 for BMI ≥30.0; P trend < 0.0001). A longer time spent exercising (more than 5 h/week) showed a decreased risk for any type of breast cancer among overall and pre- and postmenopausal women, although this did not reach statistical significance. Height was not associated with any risk.
Conclusions: Higher BMI is associated with an increased risk of ER+/PgR+ cancer among women overall and postmenopausal women. PA might be associated with a decreased risk of any type. To prevent breast cancer, weight control and PA are important.