Statistical Package of Social Sciences software (version 13.0) (SPSS, Inc., Chicago, IL) was used for statistical analysis. The independent Student's t-test or ANOVA was used to compare the continuous variables between groups, whereas the x 2 test was applied for comparison of dichotomous variables. The Kaplan-Meier estimate was used for survival analysis, and the log-rank test was used to compare the cumulative survival durations in different patient groups. The level of statistical significance was set at 0.05 for all tests.