Prognostic impacts of skip metastasis in N2a and N2b subgroups of non-small cell lung cancer: insights from a large cohort

The prognostic significance of skip metastasis remains controversial in the context of the recently revised N2a (single-station) and N2b (multi-station) of non-small cell lung cancer (NSCLC). This study aims to investigate the survival impact of skip metastasis in these subgroups. We retrospectively analyzed 1,873 NSCLC patients who underwent surgery with systematic lymph node dissection at a single institution. Patients were categorized into pN1, skip pN2a, non-skip pN2a, skip pN2b, and non-skip pN2b groups. Overall survival (OS) and disease-free survival (DFS) were assessed using Kaplan-Meier analysis and Cox proportional hazards regression, with propensity score matching (PSM) and inverse probability of treatment weighting (IPTW) applied to minimize confounding. Skip metastasis was identified in 34.1% of pN2 cases, with a higher incidence in pN2a (41.3%) than in pN2b (24.3%). Skip pN2a showed significantly better 5-year OS and DFS rates compared to non-skip pN2a (72% vs. 67%, P=0.02; 57% vs. 48%, P=0.002). Similarly, skip pN2b had superior outcomes compared to non-skip pN2b (5-year OS: 65% vs. 58%, P=0.008; DFS: 42% vs. 37%, P=0.03). Notably, no significant survival difference was observed between skip pN2a and pN1, or between non-skip pN2a and skip pN2b, even after PSM and IPTW adjustments. Skip metastasis confers a survival advantage in both pN2a and pN2b NSCLC subgroups with comparable survival between skip pN2a and pN1, as well as between non-skip pN2a and skip pN2b.