Spss software package 21.0 for windows

The SPSS software package 21.0 for Windows (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis. Normally distributed continuous variables are presented as mean ± standard deviation (SD) and between‐group differences assessed using the independent t test. Non‐normally distributed continuous variables are presented in median (25% percentile, 75% percentile), and between‐group differences were assessed using the Mann–Whitney U test. Between‐group differences with respect to categorical variables were assessed using the Chi‐squared pair‐wise test. Univariate log rank test was performed to identify risk factors for mortality during hospitalization. For variables with statistical significance in the univariate analysis, a further multivariate survival analysis was performed using the Cox regression model to identify risk factors with an independent impact. A P value of <0.05 was considered statistically significant.

The study endpoints included the rates of second primary tumors, local recurrence, neck recurrence, distant metastases, disease-free survival, disease-specific survival, and overall survival. Overall survival and disease-specific survival were calculated from the date of primary surgery to the date of death from any cause and OSCC, respectively. Disease-free survival was measured as the time elapsed from the date of primary surgery to the date of tumor relapse. The rates of local recurrence, neck recurrence and distant metastases were calculated from the date of surgery to the date of local, neck, and distant events, respectively. Survival curves were plotted using the Kaplan-–Meier method and compared using the log-rank test. Multivariate hazard ratios for time-to-event outcomes were calculated using forward stepwise Cox regression models. The association between HPV infection status and CNA in each target region was analyzed using the χ² test. All statistical calculations were performed using R package and the SPSS software package 21.0 for Windows (SPSS Inc., Chicago, Illinois, USA).