Nomogram calibration and validation
The C-index was used to compare the performance of the nomograms. Particularly, the C-index of the training cohort without stratification by age and the validation cohort was 0.79 (95% CI 0.77–0.81) and 0.81 (95% CI 0.77–0.84), respectively. In the early-onset COCA training set cohort, validation cohort C-index was 0.95 (95% CI 0.91–0.99), 1. In the late-onset COCA training cohort, the validation cohort C-index was 0.72 (95% CI 0.69–0.75), 0.75 (95% CI 0.71–0.79), respectively. The C-index of the nomogram for predicting the OS of patients grouped by the TNM staging based on the 8th edition of AJCC guidelines was 0.68 (95% CI 0.65–0.71). ROC curves were plotted to assess the performance of the models (Fig. ROC for the 6- and 18-month prognosis prediction of the nomograms and the TNM staging system. Calibration curves of the nomogram and TNM staging system. 