Statistical analysis
We analyzed the corresponding continuous variables by the Mann-Whitney U-test, the Χ2 test, Kaplan-Meier curve analysis, the log-rank test, multivariate Cox regression and other methods. Based on the unvaried analysis, variables with P< 0.05 were included in the multivariate logistic regression analysis to determine the independent variables. All analyses were performed using SPSS 23.0 statistical software (SPSS, IL, USA). P< 0.05 was considered statistically significant.