Postmenopausal endometrial cancer risk and body size in early life and middle age: prospective cohort study.

BACKGROUND: Greater adiposity in early life has been linked to increased endometrial cancer risk in later life, but the extent to which this association is mediated through adiposity in later life is unclear. METHODS: Among postmenopausal women who had never used menopausal hormone therapies and reported not having had a hysterectomy, adjusted relative risks (RRs) of endometrial cancer were estimated using Cox regression. RESULTS: Among 249 791 postmenopausal women with 7.3 years of follow-up on average (1.8 million person-years), endometrial cancer risk (n=1410 cases) was strongly associated with current body mass index (BMI) at baseline (RR=1.87 per 5 kg m(-2) increase in BMI, 95% confidence interval (CI): 1.77-1.96). Compared with women thinner than average at age 10, the increased risk among women plumper at age 10 (RR=1.27, 95% CI: 1.09-1.49) disappeared after adjustment for current BMI (RR=0.90, 95% CI: 0.77-1.06). Similarly, compared with women with clothes size 12 or less at age 20, the increased risk among women with clothes size 16 or larger (RR=1.87, 95% CI: 1.61-2.18) was not significant after adjustment for current BMI (RR=1.03, 95% CI: 0.88-1.22). CONCLUSION: Among women who have never used hormone therapy for menopause, the association between body size in early life and endometrial cancer risk in postmenopausal women can be largely explained by women's current BMI.