Validation of the 8th edition of AJCC/UICC staging system for nasopharyngeal carcinoma: Results from a non-endemic cohort with 10-year follow-up

Objectives: This study aimed to validate the 8th edition of American Joint Committee on Cancer/Union for International Cancer Control (AJCC/UICC) TNM staging system for nasopharyngeal carcinoma (NPC) in non-endemic region. Materials and methods: We recruited 607 patients with histology-proven, previously untreated, non-metastatic NPC treated by intensity-modulated radiotherapy (IMRT) at our center. Harrell's concordance index (c-index) and Akaike information criterion (AIC) were applied to compare the prognostic discrimination between the 7th and 8th edition staging system. Results: For T category, the local recurrence-free survival (LRFS) Kaplan-Meier curves of T1, T2 and T3 were well separated in the 8th edition; however, LRFS did not significantly differ between T3 and T4 (P = 0.166). Moreover, the 7th edition achieved higher c-index (0.702 [95% CI, 0.618-0.787] vs. 0.685 [95% CI, 0.604-0.767]) and lower AIC (766.1 vs. 770.8) than 8th edition for LRFS. With regard to N category, the 8th edition achieved higher c-index (0.796 [95% CI, 0.749-0.843] vs. 0.751 [95% CI, 0.696-0.805]) and lower AIC (1439.4 vs. 1471.9) for distant metastasis-free survival. In terms of overall stage, the 8th edition also had higher c-index (0.798 [95% CI, 0.753-0.844] vs. 0.721 [95% CI, 0.672-0.770]) and lower AIC (1963.9 vs. 2007.2) compared with the 7th edition for overall survival. Furthermore, interval validation by bootstrapping the sample randomly for similar to 100-1000 times also validated above findings. Conclusion: The 8th edition of AJCC/UICC TNM staging system achieved significantly better prognostic discrimination than the 7th edition with regard to N category and overall stage but not T category.