BMI change and abdominal circumference are risk factors for breast cancer, even in Asian women

Purpose We investigated the association between breast cancer incidence and obesity among Asian women. Methods We used data from 30,109 women who had undergone medical check-ups and opportunistic breast cancer screening at least twice at the St. Luke's International Hospital Affiliated Clinic, Center for Preventive Medicine, between April 1, 2005 and March 31, 2014. This study evaluated obesity through body mass index (BMI) at age 18-20 years (BMI18-20y), BMI at research entry (entry BMI), change of BMI from age 18-20 to research entry (Delta BMI), abdominal circumference at research entry (AC), and HbA1c [N] at research entry (HbA1c). We used a multivariate Cox proportional hazard model to evaluate hazard ratios (HRs) and 95% confidence intervals (95% CIs). Results Of the 30,109 women, 325 were initially diagnosed with breast cancer over 131,657 person-years. Postmenopausal women whose BMI increased >=+5.0 were significantly more likely to develop breast cancer (HR 1.902, 95% CI 1.202-3.009) than were the stable BMI group (Delta BMI: -2.5 to +2.5). Postmenopausal women with AC >= 90 cm were significantly likelier to develop breast cancer than were those with AC < 70 cm (HR 2.500, 95% CI 1.091-5.730). Among postmenopausal women whose BMI18-20y was >= 20, those with high (>= 6.5) HbA1c were more likely to develop breast cancer than those with low (< 5.5) HbA1c (HR 3.325, 95% CI 1.307-8.460). Conclusions Breast cancer incidence and obesity are positively associated in postmenopausal Asian women.