Promising treatment outcomes of intensity-modulated radiation therapy for nasopharyngeal carcinoma patients with N0 disease according to the seventh edition of the AJCC staging system

BACKGROUND: Intensity-modulated radiation therapy (IMRT) provides excellent locoregional control for nasopharyngeal carcinoma (NPC), and has gradually replaced two-dimensional conventional radiotherapy as the first-line radiotherapy technique. Furthermore, in the new seventh edition of the American Joint Committee on Cancer (AJCC) staging system, retropharyngeal lymph nodes were upgraded from N0 to N1 disease as a result of their negative impact on the distant metastasis-free survival (DMFS) rates of NPC. This retrospective study was conducted in order to review the treatment outcomes and patterns of failure in NPC patients with N0 disease after IMRT in order to effectively guide treatment in the future. METHODS: We retrospectively reviewed data from 506 biopsy-proven nonmetastatic NPC patients. There were 191 patients with negative cervical lymph node involvement. According to the seventh edition of the American Joint Committee on Cancer (AJCC) staging system, 110 patients (21.7%) were staged with N0 disease, and 81 patients (16.0%) were reclassified with N1 disease due to the presence of RLN metastasis. All patients received IMRT as the primary treatment. RESULTS: In patients with negative cervical lymph node involvement, distant metastasis-free survival (DMFS) was significantly higher in patients without retropharyngeal lymph node (RLN) metastasis than those with RLN metastasis (95.9% vs. 88.1% respectively, P = 0.04). For N0 disease, the 5-year overall survival (OS), local relapse-free survival (LRFS), nodal relapse-free survival (NRFS) and DMFS rates were 93.8%, 97.1%, 99.1% and 95.9%, respectively. For T1N0, T2N0, T3N0 and T4N0, OS was 97.8%, 100%, 93.8% and 76.9%, LRFS was 100%, 92.9%, 100% and 88.9% and DMFS was 96.6%, 90.9%, 100% and 93.3%, respectively. OS and LRFS were higher in T1-3 N0 patients than T4N0 patients (P < 0.01 and P = 0.01, respectively). CONCLUSIONS: The seventh edition of the AJCC N-staging system improves prognostic accuracy by upgrading RLN metastasis to N1 disease. IMRT produces excellent survival rates in T1-3 N0 disease; however, T4N0 disease remains a challenge and additional improvements are required to achieve a favorable prognosis for these NPC patients.