Head and neck MRI-based T stage and [F]FDG PET/CT-based N/M stage improved prognostic stratification in primary nasopharyngeal carcinoma.

Objectives: To evaluate whether MRI-based T stage (T), [F]FDG PET/CT-based N (N), and M stage (M) are superior in NPC patients' prognostic stratification based on long-term survival evidences, and whether TNM staging method involving T + N + M could improve NPC patients' prognostic stratification.

Methods: From April 2007 to December 2013, 1013 consecutive untreated NPC patients with complete imaging data were enrolled. All patients' initial stages were repeated based on (1) the NCCN guideline recommended "T + N + M" ("MMP") staging method; (2) the traditional "T + N + M" ("MMC") staging method; (3) the single-step "T + N + M" ("PPP") staging method; or (4) the "T + N + M" ("MPP") staging method recommended in present research. Survival curve, ROC curve, and net reclassification improvement (NRI) analysis were used to evaluate the prognosis predicting ability of different staging methods.

Results: [F]FDG PET/CT performed worse on T stage (NRI =  - 0.174, p < 0.001) but better on N (NRI = 0.135, p = 0.004) and M stage (NRI = 0.126, p = 0.001). The patients whose N stage upgraded by [F]FDG PET/CT had worse survival (p = 0.011). The "T + N + M" ("MPP") method performed better on survival prediction when compared with "MMP" (NRI = 0.079, p = 0.007), "MMC" (NRI = 0.190, p < 0.001), or "PPP" method (NRI = 0.107, p < 0.001). The "T + N + M" ("MPP") method could reclassify patients' TNM stage to a more appropriate stage. The improvement is significant in patients with more than 2.5-years follow-up according to the time-dependent NRI values.

Conclusions: The MRI is superior to [F]FDG PET/CT in T stage, and [F]FDG PET/CT is superior to CWU in N/M stage. The "T + N + M" ("MPP") staging method could significantly improve NPC patients' long-term prognostic stratification.

Clinical Relevance Statement: The present research provided long-term follow-up evidence for benefits of MRI and [F]FDG PET/CT in TNM staging for nasopharyngeal carcinoma, and proposes a new imaging procedure for TNM staging incorporating MRI-based T stage and [F]FDG PET/CT-based N and M stage, which significantly improves long-term prognostic stratification for patients with NPC.

Key Points: • The long-term follow-up evidence of a large-scale cohort was provided to evaluate the advantages of MRI, [F]FDG PET/CT, and CWU in the TNM staging of nasopharyngeal carcinoma. • A new imaging procedure for TNM stage of nasopharyngeal carcinoma was proposed.