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Purpose:To evaluate the prognostic value of variables including nodal size, level, laterality, extranodal neoplastic spread (ENS), and necrosis in patients with nasopharyngeal carcinoma (NPC) and further explore the feasibility of an N-staging system using Radiation Therapy Oncology Group (RTOG) guidelines for lymph node levels based on magnetic resonance imaging (MRI). Experimental Design: The MRI scans of 924 patients with histologically diagnosed nondisseminated NPC were reviewed retrospectively. The distribution of the tumors was mapped using RTOG guidelines and laterality. The multiplicity of each tumor was calculated, as well as the size and status of ENS and the necrosis of individual nodes. Results: Nodal level, cervical lymph node laterality, and ENS were independent prognostic factors for disease failure and distant failure in multivariate analyses. There was no significant difference in the hazard ratios (HR) for distant failure between level II and retropharyngeal, level Ib, levelV, or level III involvement, whereas patients with level IVand supraclavicular fossa involvement had a significant increase in HRs. The subsets that made up a given N stage group had similar HRs for distant failure. Both the HRs for disease failure and distant failure by the proposed N staging system between one stage and the next were statistically significant (P < 0.05). The survival curves of disease-free survival and distant metastasis-free survival for all subclassifications of N stage showed significant difference from the adjacent stage (P < 0.05). The overall distribution pattern of the proposed N staging was more equitable than that of the 6th American Joint Committee on Cancer N staging. Conclusions: Nodal variables including level, cervical lymph node laterality, and ENS are independent prognostic factors for NPC. The proposed N staging system of NPC using RTOG guidelines based on MRI is highly predictive and may provide a more objective method for staging NPCs.

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