Statistical analysis
All continuous data were expressed as means ± standard deviation, medians (quartile: 25-75%), or numbers (expressed as percentage, %). The comparison between groups was analyzed using univariate (unpaired Student’s t -test and Fisher’s exact test) and multivariate analyses with a Cox hazard model. A p -value of < 0.05 was considered statistically significant. Recurrence curves were plotted using the Kaplan-Meier method. All statistical analyses were performed with R commander, which is a graphical user interface for R (Saitama Medical Center, Jichi Medical University, Saitama, Japan).