External validity of a prognostic nomogram for locoregionally advanced nasopharyngeal carcinoma based on the 8th edition of the AJCC/UICC staging system: a retrospective cohort study

Abstract Background The tumor–node–metastasis (TNM) staging system does not perform well for guiding individualized induction or adjuvant chemotherapy for patients with locoregionally advanced nasopharyngeal carcinoma (NPC). We attempted to externally validate the Pan’s nomogram, developed based on the 8th edition of the American Joint Committee on Cancer (AJCC)/Union for International Cancer Control (UICC) staging system, for patients with locoregionally advanced disease. In addition, we investigated the reliability of Pan’s nomogram for selection of participants in future clinical trials. Methods This study included 535 patients with locoregionally advanced NPC who were treated between March 2007 and January 2012. The 5-year overall survival (OS) rates were calculated using the Kaplan–Meier method and compared with predicted outcomes. The calibration was tested using calibration plots and the Hosmer–Lemeshow test. Discrimination ability, which was assessed using the concordance index, as compared with other predictors. Results Pan’s nomogram was observed to underestimate the 5-year OS of the entire cohort by 8.65% [95% confidence interval (CI) − 9.70 to − 7.60%, P