The area under the ROC curve was 0.820 for the simplified TNS score for No. 10 LN metastasis. Compared with tumor size, preoperative N staging or the preoperative T staging, the TNS score more accurately predicts No.10 LN metastasis (Figure 3). The incidence rates observed in the validation set were compared to the predicted incidence rates to evaluate the model performance. The ratio of the expected to observed risk of No. 10 LN metastasis was 1.49, (χ2 = 0.84, P = 0.359), indicating good calibration. The ratios of the expected to observed risks for the low-, intermediate-, and high-risk categories in the validation set were 1.56, 1.08, and 2.09, respectively. There were no statistically significant differences among the groups (Table 6).