Comparison of TNM staging systems for nasopharyngeal carcinoma, and proposal of a new staging system

Background: There are few systematic evaluations regarding the sixth and seventh editions of the UICC/AJCC TNM Staging System (TNM6th, TNM7th) and Chinese 2008 Staging System (TNMc2008) for nasopharyngeal carcinoma (NPC). Methods: We classified 2333 patients into intensity-modulated radiotherapy (IMRT) cohort (n = 941) and conventional radiotherapy (CRT) cohort (n = 1392). Tumour staging defined by TNM6th, TNM7th and TNMc2008 was compared based on Akaike information criterion (AIC) and Harrell's concordance index (c-index). Results: For T-classification, TNM6th (AIC = 2585.367; c-index = 0.6390385) had superior prognostic value to TNM7th (AIC = 2593.242; c-index 0.6226889) and TNMc2008 (AIC = 2593.998; c-index = 0.6237146) in the IMRT cohort, whereas TNMc2008 was superior (AIC = 5999.054; c-index = 0.623547) in the CRT cohort. For N-classification, TNMc2008 had the highest prognostic value in both cohorts (AIC = 2577.726, c-index = 0.6297874; AIC = 5956.339, c-index = 0.6533576). Similar results were obtained when patients were stratified by chemotherapy types, age and gender. Using staging models in the IMRT cohort, we failed to identify better stage migrations than TNM6th T-classification and TNMc2008 N-classification. We therefore proposed to combine these categories; resultantly, stage groups of the proposed staging system showed superior prognostic value over TNM6th, TNM7th and TNMc2008. Conclusion: TNM6th T-classification and TNMc2008 N-classification have superior prognostic value in the IMRT era. By combining them with slight modifications, TNM criteria can be unified and its prognostic value be improved.