Prediagnostic body size and breast cancer survival in the E3N cohort study

Obesity has been associated with poor breast cancer prognosis, however most studies have focused on body mass index (BMI) and few have considered the distribution of adipose tissue. We investigated associations between prediagnostic adiposity and breast cancer survival, considering BMI, waist and hip circumferences (WC and HC), and waist-to-hip ratio (WHR). Analyses included 3,006 women from the French E3N prospective cohort study diagnosed with primary invasive breast cancer between 1995 and 2008. We investigated overall, breast cancer-specific, and disease-free survival, overall and according to stage, menopausal and hormonal status and year of diagnosis, using Cox proportional hazard models adjusted for tumor characteristics and lifestyle risk factors. Women with a prediagnostic HC > 100 cm were at increased risk of death from all causes (hazard ratio (HR)>100 vs < 95 cm  = 1.38, 95% Confidence Interval (CI) = 1.02-1.86, Ptrend  = 0.02) and from breast cancer (HR>100 vs < 95 cm  = 1.50, CI = 1.03-2.17, Ptrend  = 0.03), and of second invasive cancer event (HR>100 vs < 95 cm  = 1.36, CI = 1.11-1.67, Ptrend  = 0.002), compared to those with HC <95 cm. Associations were stronger after adjustment for BMI. BMI, WC and WHR were not associated with survival after breast cancer. Our study underlines the importance of going beyond BMI when studying the association between adiposity and breast cancer survival. Further studies should be conducted to confirm our results on hip circumference.