Prognostic value of radiologic extranodal extension and its potential role in future N classification for nasopharyngeal carcinoma

Purpose: We evaluated the prognostic value of various grades of radiologic extranodal extension (rENE) and their potential roles in N-classification refinement for nasopharyngeal carcinoma (NPC). Methods and Materials: All NPC patients treated with IMRT in our institution between 2005 and 2011 were included. Pre-treatment MR of cN + cases were reviewed and rENE was recorded asGO: lymph nodes (LNs) without rENE; Gl: tumor infiltrating beyond individual nodal capsule(s) into the surrounding fat plane; G2: coalescent nodal mass with unequivocal evidence of rENE; G3: tumor infiltrating beyond nodal capsule into adjacent structures. Multivariable analysis (MVA) assessed prognostic value of rENE for distant metastasis (DM) and death adjusted for age, gender, LDH, T-classification, N-classification, and chemotherapy cycles. Results: A total of 1390 of 1616 (86%) NPC were cN +, and rENE was detected in 826/1390 (59%) patients: 256 (18.4%) Gl-rENE, 487 (35%) G2-rENE, and 83 (6%) G3-rENE. MVA confirmed that G2-/G3-rENE had increased risk of DM (HR: 2.05/3.18, both p < 0.001) and death (HR: 1.62/2.39, p = 0.002/p < 0.001), while G1-rENE was non-prognostic (DM: p = 0.172; death: p = 0.320). We propose a refined N: New-N1: N1/N2 without G2-/G3-rENE; New-N2: N1_G2-rENE; New-N3: N2_G2-rENE, N1/N2_G3-rENE, or N3. The New-N classification had a lower AIC and higher c-index for DM (AIC: 3809.6 vs 3830.9; c-index: 0.700 vs. 0.677) and death (AIC: 3693.8 vs. 3705.9; c-index: 0.735 vs. 0.725) versus TNM-8 N. Conclusions: G2- and G3-rENE are independently prognostic for DM and death in NPC. Compared to the TNM8 N-classification, a refined N-classification incorporating G2- and G3-rENE improves prognostication of DM and mortality risk.