Suggestions for lymph node classification of UICC/AJCC staging system: a retrospective study based on 1197 nasopharyngeal carcinoma patients treated with intensity-modulated radiation therapy

Abstract

This article provides suggestions for N classification of Union for International Cancer Control/American Joint Committee on Cancer (UICC/AJCC) staging system of nasopharyngeal carcinoma (NPC), purely based on magnetic resonance imaging (MRI) in intensity-modulated radiation therapy (IMRT) era.A total of 1197 nonmetastatic NPC patients treated with IMRT were enrolled, and all were scanned by MRI at nasopharynx and neck before treatment. MRI-based nodal variables including level, laterality, maximal axial diameter (MAD), extracapsular spread (ECS), and necrosis were analyzed as potential prognostic factors. Modifications of N classification were then proposed and verified.Only nodal level and laterality were considered to be significant variables affecting the treatment outcome. N classification was thus proposed accordingly: N0, no regional lymph node (LN) metastasis; N1, retropharyngeal LNs involvement (regardless of laterality), and/or unilateral levels I, II, III, and/or Va involvement; N2, bilateral levels I, II, III, and/or Va involvement; and N3, levels IV, Vb, and Vc involvement. This proposal showed significant predicting value in multivariate analysis. N3 patients indicated relatively inferior overall survival (OS) and distant metastasis-free survival (DMFS) than N2 patients; however, the difference showed no statistical significance (P = 0.673 and 0.265 for OS and DMFS, respectively), and this was considered to be correlated with the small sample sizes of N3 patients (79 patients, 6.6%).Nodal level and laterality, but not MAD, ECS, and necrosis, were considered to be significant predicting factors for NPC. The proposed N classification was proved to be powerfully predictive in our cohort; however, treatment outcome of the proposed N2 and N3 patients could not differ significantly from each other. This insignificance may be because of the small sample sizes of N3 patients. Our results are based on a single-center data, to develop a new N classification that is universally acceptable; further verification by data from multicenter is warranted.

FIGURE 1

Proposal A. (A) N distribution. (B) Distant metastasis-free survival. (C) Regional relapse-free survival. (D) Overall survival.

FIGURE 2

Proposal B. (A) N distribution. (B) Distant metastasis-free survival. (C) Regional relapse-free survival. (D) Overall survival.

FIGURE 3

Representative MRI imaging pictures of three patients with N1 (A and B), N2 (C and D), and N3 (E and F). (A), (C), and (E) applied T2-weighted axial MRI scan; (B), (D), and (F) used coronal T2-weighted STIR scan. (A) and (B) showed lymph node involvement in right level III, with central necrosis; (C) and (D) demonstrated bilateral lymph nodes involvement in levels II (bilateral) and III (left); and (E) and (F) illustrated lymph nodes involvement in right levels II–IV. MRI = magnetic resonance imaging, STIR = short time inversion recovery.