Added value of metastatic cervical lymph node group V in nodal staging of nasopharyngeal cancer

Background: Prognostic significance of posterior cervical lymph node metastasis in nasopharyngeal cancer is largely unknown. This study aims to determine the added prognostic significance of cervical lymph node group V to the standard American Joint Committee on Cancer (AJCC) staging system (eighth edition AJCC) of nasopharyngeal patients with cancer treated with intensity-modulated radiation therapy (IMRT) in terms of overall survival (OS), distant metastatic-free survival (DMFS), and disease-free survival (DFS). Methods and Materials: A retrospective cohort of 199 consecutively diagnosed nasopharyngeal patients with cancer treated with definitive radiotherapy (RT) or concurrent chemoradiotherapy (CCRT) in the era of IMRT in a large university hospital in endemic area of Southeast Asia. Pre-treatment imaging studies were thoroughly re-evaluated and re-staged by a board-certified radiologist using radiographic criteria for cervical lymph node metastasis. T and N classifications were reclassified according to the eighth AJCC staging system. Group V (Va and Vb) cervical node was evaluated for its added prognostic significance. Cox's proportional hazard model was used to retrieve hazard ratio (HR), 95% confidence interval and P value for N classification. Harrell's C-statistic (concordance index) was used for test of discrimination and internal validation was calculated by bootstrap method. Results: This study demonstrated greater separation of OS with HR of 6.75 (95%CI 1.94-23.51, P =.003) by using group Vb only as N3 compared to HR of 4.70 (95%CI 1.37-16.13, P =.014) by using current standard N3 disease (groups IV and Vb). Similarly, N2 with presence of Va shows worsened DFS with HR of 8.70 (95%CI 1.08-69.67, P =.042) compared to N2 without Va with HR of 5.93 (95%CI 0.76-46.00, P =.089). After incorporating cervical group V into nodal staging, the HR and 95%CI among each group was better separated than the eighth AJCC staging system but without significant improvement in C-index. Conclusion: Cervical lymph node group V is a potentially added prognostic factor to standard TNM staging.