Statistical analyses

Continuous data are expressed as means with standard deviations and categorical data as frequencies and percentages. Continuous variables were analyzed using Student’s t-test, and categorical variables were analyzed using the chi-square test or Fisher’s exact test. The survival rate was analyzed using the Kaplan-Meier method. The log-rank test was used to assess statistical significance. A stepwise multivariable Cox proportional hazards model was used among statistically significant variables (P<0.05) in the univariate model. Multivariable analysis was performed using Cox’s proportional hazards regression model to evaluate the effects of multiple variables on survival and late recurrence. A P value less than 0.05 was considered to indicate statistical significance. SPSS ver. 25.0 (SPSS Inc., Chicago, IL, USA) was used to perform the statistical analyses.