Body mass index at the time of diagnosis and the risk of advanced stages and poorly differentiated cancers of the breast: findings from a case-series study

Introduction: Obesity is a risk factor for postmenopausal breast cancer and is independently associated with shorter disease-free and overall survival. Currently, in clinical settings, the combination of stage and grade of cancer at the initial presentation of the disease is the best prognostic indicator. Objective: To evaluate the association between body mass index (BMI) and risk of advanced stages and poorly differentiated grade of breast cancer. Design: A case-series study of women diagnosed with their first primary invasive breast cancer. Patients include a total of 831 women aged >= 40 years with a mean BMI of 29.6(+/- 6.6) kg m(-2). Pathological, clinical and demographic data were retrieved from electronic medical records. Multinomial logistic regression analysis was preformed to estimate the risk of more advanced stages and poorly differentiated grade of cancer, adjusting for covariates. Results: Obese compared with normal weight women had an 80% increased risk of cancer with more advanced stages (III/IV) and poorly differentiated grade (odds ratio = 1.80, 95% confidence interval 1.13-2.86, P = 0.014). No significant increase in risk was observed for overweight women. Conclusion: Obesity at the time of diagnosis of breast cancer is associated with more advanced stages and poorly differentiated grade of cancers. International Journal of Obesity (2010) 34, 1381-1386; doi: 10.1038/ijo.2010.69; published online 30 March 2010