MRI‐Based Metastatic Nodal Number and Associated Nomogram Improve Stratification of Nasopharyngeal Carcinoma Patients: Potential Indications for Individual Induction Chemotherapy

Background Metastatic lymph nodal number (LNN) is associated with the survival of nasopharyngeal carcinoma (NPC); however, counting multiple nodes is cumbersome. Purpose To explore LNN threshold and evaluate its use in risk stratification and induction chemotherapy (IC) indication. Study Type Retrospective. Population A total of 792 radiotherapy‐treated NPC patients (N classification: N0 182, N1 438, N2 113, N3 59; training group: 396, validation group: 396; receiving IC: 390). Field Strength/Sequence T1‐, T2‐ and postcontrast T1‐weighted fast spin echo MRI at 1.5 or 3.0 T. Assessment Nomogram with (model B) or without (model A) LNN was constructed to evaluate the 5‐year overall (OS), distant metastasis‐free (DMFS), and progression‐free survival (PFS) for the group as a whole and N1 stage subgroup. High‐ and low‐risk groups were divided (above vs below LNN‐ or model B‐threshold); their response to IC was evaluated among advanced patients in stage III/IV. Statistical Tests Maximally selected rank, univariate and multivariable Cox analysis identified the optimal LNN threshold and other variables. Harrell's concordance index (C‐index) and 2‐fold cross‐validation evaluated discriminative ability of models. Matched‐pair analysis compared survival outcomes of adding IC or not. A P value < 0.05 was considered statistically significant. Results Median follow‐up duration was 62.1 months. LNN ≥ 4 was independently associated with decreased 5‐year DMFS, OS, and PFS in entire patients or N1 subgroup. Compared to model A, model B (adding LNN, LNN ≥ 4 vs <4) presented superior C‐indexes in the training (0.755 vs 0.727) and validation groups (0.676 vs 0.642) for discriminating DMFS. High‐risk patients benefited from IC with improved post‐IC response and OS, but low‐risk patients did not ( P = 0.785 and 0.690, respectively). Conclusions LNN ≥ 4 is an independent risk stratification factor of worse survival in entire or N1 staging NPC patients. LNN ≥ 4 or the associated nomogram has potential to identify high‐risk patients requiring IC. Evidence Level 4 Technical Efficacy 4