Statistical Analyses
Statistical analyses were performed using IBM SPSS Statistics for Windows, Version 23.0. a statistical software package (Armonk, NY: IBM Corp; 2015). Frequency distribution of demographic and clinical-pathological characteristics across the groups were compared using Pearson’ s chi-square tests. For comparison of continuous variables between two groups, the Student’s t-test or Mann-Whitney U test was used, depending on whether or not the statistical hypotheses were fulfilled. Survival curves were generated using Kaplan-Meier methods, and the log-rank analysis was carried out to evaluate the survival differences between groups. All statistical tests were 2-sided, and p< 0.05 was considered statistically significant.