Prognostic value of retropharyngeal lymph node metastasis laterality in nasopharyngeal carcinoma and a proposed modification to the UICC/AJCC N staging system

Background and purpose: Metastasis laterality is used for N classification of cervical lymph nodes, but not retropharyngeal lymph nodes (RLNs). This study explored the prognostic value of laterality of RLN metastasis to provide suggestions for a better N standard classification. Materials and methods: This retrospective study evaluated 1225 patients with new biopsy-confirmed nasopharyngeal carcinoma (NPC). Univariable and multivariable Cox regression models were used to assess overall survival (OS), progression-free survival (PFS), and distant metastasis-free survival (DMFS). A new N classification system was developed and compared to the 8th AJCC system. Kaplan-Meier methods with log-rank tests were used to compare OS, PFS, and DMFS between our proposed N stage and the AJCC N stages. Results: The incidence of RLN metastasis was 38.7% (unilateral) and 27.5% (bilateral). In the N1 subgroup, metastasis laterality was associated with significant differences in the 5-year rates of OS (89.4% vs. 82.6%, p = 0.016), DMFS (91.5% vs. 82.9%, p = 0.004), and PFS (80.3% vs. 71.2%, p = 0.016). However, no significant differences in these outcomes were observed when we compared N2 disease to N1 bilateral RLN metastasis. Multivariate analysis confirmed that bilateral RLN metastasis independently predicted OS, DMFS, and PFS. The proposed classification broadened the differences in OS, DMFS, PFS between N1 and N2 disease. Conclusion: Patients with NPC and unilateral RLN metastasis had better survival than did patients with bilateral RLN metastasis. Upgrading cases with bilateral RLN metastasis from N1 to N2 may help improve prognostication using the 8th AJCC system. (C) 2019 Elsevier B.V. All rights reserved.