A Proposal of N Classification Based on Quantitative Metastatic Lymph Node Regions in Nasopharyngeal Carcinoma

Abstract

To assess the prognostic importance of the absolute number of metastatic lymph node regions (NLR) in patients with nasopharyngeal carcinoma (NPC), and to explore the feasibility of a new N classification system based on quantitative nodal regions. Magnetic resonance imaging (MRI) scans of 358 patients with histologically diagnosed non-disseminated NPC were reviewed. Tumor characteristics regarding the 8th UICC/AJCC staging system were documented, as well as additional metastatic lymph node (LN) features including extranodal spread (ENS), central necrosis, nodal distribution and NLR. Following the 2013 consensus guideline for delineation of the neck node levels for head and neck tumors, LN regions were quantified by summing up the involved subunits of VIIa (retropharyngeal nodes), I, IIa, IIb, III, IVa, IVb, Va, Vb, Vc, VI, III, IX, X. Univariate and multivariable survival analyses were performed with Cox proportional hazards models to test the prognostic value of variables. NLR showed significant correlation to other LN characteristics and N stage by 8th UICC/AJCC system (P<0.001). Univariate analysis showed that all listed nodal variables were significantly related to overall survival (OS), distant metastasis free survival (DMFS) and disease free survival (DFS). After adjusting for clinical variables such as age, sex, treatment modality etc, multivariable models revealed that only NLR and maximum LN diameter (MLD)>6cm were significant predictors for DMFS, while T category and ENS were significant for OS; MLD>6cm, NLR and ENS were significant for DFS. Based on these variables N was then categorized into: N0, no lymph node metastasis; N1, NLR 1-3, without ENS; N2, NLR 4-9, or NLR 1-3 with ENS; N3, NLR≥10 or MLD>6cm. This classification showed good and stable concordance with DMFS, OS and DFS, compared to N staging system by 8th UICC/AJCC (Table 1). NLR, as a potential surrogate for quantitative LN tumor burden, is a predominant independent prognostic factor in NPC. Integration of quantitative nodal regions may simplify N staging and warrants further validation in future.Abstract MO_44_2892; Table 1Classification of N according to 8th edition of UICC/AJCC staging system and proposed system8th edition of N stageProposed N classificationN5y-DMFS, %5y-OS, %5y-DFS, %N5y-DMFS, %5y-OS, %5y-DFS, %N01009093.1N010093.193.1N19289.984.4N192.190.485.3N280.175.763.4N285.482.070.9N373.576.961.8N360.167.448.6Overall P<.0010.011<.001Overall P<.001<.001<.001Abbreviations: DMFS = distant metastasis free survival; OS = overall Survival; DFS = disease free survival. Open table in a new tab