Supplementary Material for: Construction of Prognostic Nomogram in Patients with N3-stage Nasopharyngeal Carcinoma

Introduction: To retrospectively identify the metastatic influence factors and predict the prognosis, and develop an individualized prognostic prediction model for patients with N3-stage nasopharyngeal carcinoma (NPC). Methods: The study collected 446 NPC patients with N3-stage from the Surveillance, Epidemiology, and End Results (SEER) database between 2010 and 2015. The patients were classified into subgroups based on the histological types and metastatic status. Multivariable logistic, Cox regression, and Kaplan-Meier (K-M) method with the log-rank test were performed. The nomogram model was created using the prognostic factors identified from Cox regression analysis. The predictive accuracy was determined based on the concordance index (c-index) and calibration curves. Results: The five-year overall survival (OS) of the NPC patients with N3-stage was 43.9%, and the prognosis of patients without any distant metastases was largely longer than that with metastases. No difference was observed between different pathological types in the entire cohort. However, patients with non-keratinized squamous cell carcinoma (NKSCC) had a better OS than that of the patients with keratinized squamous cell carcinoma (KSCC) in a nonmetastatic subgroup. Using the Cox regression analysis results, the nomogram successfully classified these patients into low- and high-risk subgroups and presented the survival difference. The c-index of the nomogram for predicting the prognosis was satisfactory. Discussion/Conclusion: This study identified metastatic risk factors and developed a convenient clinical tool for the prognosis of NPC patients. This tool can be used for individualized risk classification and decision-making regarding treatment of NPC patients with N3-stage.