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

Background:The tumor-node-metastasis(TNM)staging system does not perform well for guiding individualized induc-tion 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%confi-dence interval(CI)−9.70 to−7.60%,P<0.001]and underestimated the 5-year OS of each risk group.The differences between the predicted and observed 5-year OS rates were smallest among low-risk patients(<135 points calculated using Pan’s nomogram;which predicted minus observed OS,−6.41%,95%CI−6.75 to−6.07%,P<0.001)and were largest among high-risk patients(≥160 points)(−13.56%,95%CI−15.48 to−11.63%,P<0.001).The Hosmer-Lemeshow test suggested that the predicted and observed 5-year OS rates had no ideal relationship(P<0.001).Pan’s nomogram had better discriminatory ability compared with the levels of Epstein-Barr virus DNA acid(EBV DNA)and the 7th or 8th AJCC/UICC staging system,although not better compared with the combination of EBV DNA and the 8th staging system.Additionally,Pan’s nomogram was marginally inferior to our predictive model,which included the 8th AJCC/UICC N-classification,age,gross primary tumor volume,lactate dehydrogenase,and body mass index.Conclusions:Pan’s nomogram underestimated the 5-year OS of patients with locoregionally advanced NPC at our cancer center,and may not be a precise tool for selecting participants for clinical trials.