Outcomes After Incomplete N1 Versus N2 Nodal Evaluation in Stage I Non-Small Cell Lung Cancer.

BACKGROUND: Adequate lymph node (LN) sampling is essential in early-stage non-small cell lung cancer (NSCLC), with guidelines recommending ≥4 stations including one N1 and three N2 stations. While inadequate sampling is linked to poor outcomes, the distinct impact of missed N1 versus N2 stations remains unclear. METHODS: We conducted a retrospective cohort study of 4,227 Veterans with clinical stage I NSCLC who underwent resection at 121 Veterans Affairs medical centers (2006-2024) with exactly one missed LN station. Patients were stratified by missed N1 versus N2 station. Overall survival (OS) and cumulative incidence of recurrence (CIR) were assessed using Kaplan-Meier and multivariable Cox and Fine-Gray competing-risk models. RESULTS: Of 4,227 patients (mean age 68.2 years; 95.2% male), 11.8% had a missed N1 station and 88.2% a missed N2 station. Overall, 20.2% underwent wedge resection and 56.6% were treated minimally invasively. Missed N1 stations were more frequent with wedge resection (54.5% vs. 15.6%, p<0.0001) and less often pathologically upstaged (10.5% vs. 15.5%, p=0.003). Missed N1 station was associated with worse OS (5-year 53.6% vs. 64.4%, p<0.0001; aHR 1.30, 95% CI 1.14-1.48). CIR was higher with missed N1 station on univariate (5-year 28.4% vs. 23.9%, p=0.040) but attenuated after multivariable adjustment. CONCLUSIONS: Among early-stage NSCLC patients with incomplete LN evaluation, missed N1 stations showed less pathologic upstaging yet worse OS, consistent with occult nodal disease and potential omission of indicated adjuvant therapy. The higher frequency during wedge resection underscores the importance of complete hilar assessment during sublobar resection.