Validation and calibration of the model
The final model was subjected to 100 bootstraps resamples of the training data set and the external validation data set for internal and external validation respectively. The results of both internal and external validation were shown by the receiver operating characteristic (ROC) curve, concordance index (C-index), and Brier Score. The value of the C-index, which infers the area under the curve (AUC), ranges from 0.5 to 1.0. As 0.5 means a random chance and 1.0 means the model had a fully correct differentiating ability, it can be applied to assess the predicting ability of the final model. The value of the Brier Score ranges from 0 to 1.0, with higher values indicating better accuracy of the predicting model. To perform the calibration of the model for 1-year PFS, the predicted survival was compared with the observed survival.