Validation of a nomogram predicting complications after esophagectomy for cancer
Background: A nomogram has been developed recently in order to predict the occurrence and severity of postoperative complications after esophagectomy for cancer. In the present study, we externally validated this nomogram in a new cohort of patients who underwent esophagectomy for cancer in a different high-volume center. Methods: An independent dataset of 777 patients who underwent esophagectomy for cancer was used for validation. The discriminatory capability of the nomogram was determined by using the concordance index (C statistic). Calibration was evaluated by comparing the observed with the expected number of patients with complications, as predicted by the original nomogram across patients with different risk profiles. We also examined whether adjusting the value of the original coefficients of the predictors or adding new predictors would improve the fit of the nomogram. Results: Discrimination of the original nomogram was similar in the validation cohort: the C statistic hardly decreased from 0.65 in the original cohort to 0.64 in the validation cohort. Observed and expected number of patients with complications were in close agreement, reflecting a good calibration (p = 0.84). Reestimation of the coefficients in the validation cohort did not lead to any significant changes of the original nomogram values. Conclusions: External validation of a nomogram predicting the occurrence and severity of complications after esophagectomy showed that the model is applicable in other high-volume hospitals. Nevertheless, preoperative prediction of complications in individual patients remains difficult, most likely due to the complexity of mechanisms causing these complications.