Statistical analysis
REGRESSION
Continuous variables such as gender were shown as frequency (%), while categorical variables such as age were shown as median (range).Pearson's chi-square test was used for categorical variables to compare population characteristics, while the independent t-test (or Mann–Whitney U-test) was used for continuous variables. The Kaplan–Meier method was used to estimate the survival and the stratified log-rank test was used to evaluate any survival differences. The univariate and multivariate Cox Proportional Hazard Regression Model was applied to estimate the hazard ratio (HR) and the corresponding 95% confidential interval (CI) for every potential prognostic variable. Significant variables in univariate analyses (Based on the results of the multivariable analyses, the nomogram was created using the survival and rms packages of R 3.6.0. Discrimination evaluation and calibration evaluation were applied to assess the accuracy of the nomogram. The discrimination evaluation focused on the model’s ability to distinguish patients with different outcomes. Therefore concordance index (C-index) was used as the measuring tool. The calibration evaluation concentrated on how close the predicted probabilities were to the actual outcomes. Calibration plots of the nomogram for 3-, 5- year OS were performed in the training cohorts, internal validation cohorts, and external validation cohort. Decision curve analyses (DCA) was performed to test the reliability of the model and evaluate alternative diagnostic or prognostic tools with superiority.