Statistical analysis

Clinicopathological variables were compared between four BMI groups (underweight, normal, overweight, and obese). Differences in clinical and pathological characteristics between groups were estimated using Student’s t-test, Wilcoxon signed-rank test, and Chi-square test. Then, the patients were divided into two groups: the underweight/obese group and normal/overweight group. Kaplan-Meier survival curves were generated for OS and CSS in these two BMI groups, and compared using the log–rank test. To identify predictive factors of OS and CSS, univariable and multivariate Cox regression models were performed using all the variables collected. All statistical tests were two-tailed, and P<0.05 was considered significant. Correlations of variables with outcomes were expressed as hazard ratio (HR) with 95% confidence interval (CI). All statistical analyses were performed with SPSS 20.0 (SPSS Inc., Chicago, IL, USA).