Body weight in early adulthood, adult weight gain, and risk of endometrial cancer in women not using postmenopausal hormones

High body mass index (BMI) measured in middle age or later is an established risk factor for endometrial cancer. However, whether BMI measured in early adulthood and adult weight change are associated with endometrial cancer risk is less clear, particularly among nonusers of postmenopausal hormones (PMH). These associations were investigated among women in the Cancer Prevention Study II Nutrition Cohort. Women taking PMH (n = 11,624, 12 % of all women) were excluded, and the analysis was limited to 33,057 postmenopausal women who did not take PMH. Between enrollment in 1992/1993 and 30 June 2009, 447 women were diagnosed with endometrial cancer. Cox proportional hazards regression was used to calculate hazard rate ratios (RR) and corresponding 95 % confidence intervals (CI) for the association of BMI at age 18, calculated from recalled weight, and weight change between age 18 and 1992, with endometrial cancer incidence. BMI at age 18 was associated with higher risk of endometrial cancer in multivariable models adjusted for other risk factors (RR 1.29, 95 % CI 1.12-1.49 per 5 BMI units). Similarly, adult weight change was associated with higher risk of endometrial cancer (RR 1.81, 95 % CI 1.66-1.98 per 5 BMI unit change) in multivariable models adjusted for other risk factors. High BMI at age 18 and greater adult weight gain were strongly associated with risk of endometrial cancer. These results underscore the importance of both avoiding overweight/obesity in young adulthood and preventing weight gain thereafter to minimize risk of this cancer.