Adult lifetime body mass index trajectories and endometrial cancer risk

Objective: To identify body mass index (BMI) trajectories in adult life and to examine their association with endometrial cancer (EC) risk, also exploring whether relations differ by HRT use. Design: Pooled analysis of two case control studies. Setting: Italy and Switzerland. Population: A total of 458 EC cases and 782 controls. Methods: We performed a latent class growth model in order to identify homogenous BMI trajectories over 6 decades of age, with a polynomial function of age. Odds Ratios (ORs) and the corresponding 95% confidence intervals (CI) for EC risk were derived through a multiple logistic regression model, correcting for classification error. Main outcome measures: The relation of BMI trajectories with endometrial cancer. Results: We identified 5 BMI trajectories. Compared with women in the 'Normal weight-stable' trajectory, a reduction by about 50% in the risk of EC emerged for those in the 'Underweight increasing to normal weight' (95% CI=0.28-0.99). The 'Normal weight increasing to overweight' and the 'Overweight-stable' trajectories were associated to, respectively, an excess of 3% (95% CI=0.66-1.60) and of 71% (95% CI= 1.12-2.59) in cancer risk. The OR associated to the trajectory 'Overweight increasing to obese' was 2.03 (95% CI= 1.31-3.13). Stronger effects emerged among HRT never users (OR= 2.19 for the 'Overweight-stable' trajectory and OR=2.49 for the 'Overweight increasing to obese' trajectory). Conclusions: Our study suggests that longer exposure to overweight and obesity across lifetime is associated with an increased risk of endometrial cancer. Weight during adulthood also appears to play an important role.