Supplementary Material for: Body Mass Index at Diagnosis as a Prognostic Factor for Early-Stage Invasive Breast Cancer after Surgical Resection

<b><i>Background:</i></b> The aim of this study was to investigate the association between body mass index (BMI) and prognosis of Chinese women with breast cancer. <b><i>Patients and</i></b> <b><i>Methods:</i></b> 3,380 primary breast cancer patients who underwent surgery from 2010 to 2012 were selected and classified as low BMI group (BMI < 25.0) and high BMI group (BMI ≥ 25.0). The follow-up data for disease-free survival (DFS) and overall survival (OS) were obtained from 3,178 patients (median follow-up of 58 months). Cox regression analysis was used to evaluate the effect of BMI on DFS and OS. <b><i>Results:</i></b> The high BMI group showed more aggressive pathological features. BMI was negatively associated with OS (hazard ratio (HR) 1.33, 95% confidence interval (CI) 1.06–1.66; p = 0.012) but not DFS (HR 1.15, 95% CI 0.94–1.40; p = 0.17). Furthermore, when stratified by age, BMI was significantly and negatively associated with OS (HR 1.43, 95% CI 1.05–1.95; p = 0.025) in patients above 50 years of age, but this effect was not detected in younger patients. <b><i>Conclusion:</i></b> BMI was an independent prognostic factor of OS in Chinese women with breast cancer, and age might be a mitigating factor. Among patients above 50 years of age, those with a high BMI were at greater risk of poor prognosis compared to individuals with a low BMI.