A novel N staging system for NPC based on IMRT and RTOG guidelines for lymph node levels: Results of a prospective multicentric clinical study

The present study aimed to investigate the cervical lymph node metastasis of nasopharyngeal carcinoma (NPC) and to establish a novel N staging standard for NPC, based on intensity modulated radiation therapy (IMRT) via a prospective multicenter clinical trial. Between January 2006 and December 2009, a total of 492 patients with NPC without distant metastasis were included in the present study. All patients were treated with IMRT. According to Radiation Therapy Oncology Group division standards, the present study proposed a novel N staging system following the review of magnetic resonance images in comparison with the 7th edition of Union for International Cancer Control/American Joint Committee on Cancer (UICC/AJCC) staging system. Retropharyngeal lymph nodes, cervical lymph node level and cervical lymph node laterality were independent prognostic factors used in multivariate analyses. According to the results of the risk variety, the present study suggested that the novel N staging system included: N0 (no lymph node metastasis), N1 [retropharyngeal or/and unilateral upper cervical (I, II, III, Va, VIIb, VIII, IX and X regions) lymph node metastasis], N2 [bilateral upper cervical (I, II, III, Va, VIIb, VIII, IX and X regions) lymph node metastasis] and N3 (lymph node metastasis in IVa and Vb regions and their lower regions). The novel N staging system proposed in the present study performs better in risk difference and distribution balance. Furthermore, the differences of 5-year curves of distant metastasis-free survival and overall survival had greater statistically significant differences compared with the 7th edition of the UICC/AJCC staging system. The present study suggested a novel N staging system for cervical lymph node metastasis of NPC, which may predict the prognosis of patients with NPC in a more objective and accurate way.