BACKGROUND: Surgery is the cornerstone of treatment for early-stage non-small cell lung cancer (NSCLC). The concept of "uncertain resection" (R(un)) describes cases where complete tumor excision with clear margins is achieved but without comprehensive lymph node assessment or pleural cytology. This study aimed to establish R(un) as a prognostic factor in localized NSCLC patients and explore its heterogeneity. METHODS: This single-center retrospective study was conducted at Toulouse University Hospital. Consecutive patients who underwent surgery for localized NSCLC between 2008 and 2018 were included. Resection status, particularly R(un), was reclassified retrospectively. Overall survival and disease-free survival were analyzed, and a Cox proportional hazards regression model was used to assess whether R(un) and its newly proposed subcategories were independent predictors of survival. RESULTS: Among 1,108 patients, 732 (66.1%) were classified as R0, 291 (26.2%) as R(un), and 85 (7.7%) as R1. Our study demonstrated that R(un) was an independent prognostic factor, with adjusted hazard ratios of 1.26[95% CI: 1.03-1.52] for overall survival and 1.23[95% CI: 1.03-1.46] for disease-free survival. A proposed classification system with three R(un) subcategories revealed a continuum between uncertain and incomplete resections (p<
0.002). CONCLUSIONS: This study validated the updated resection classification for localized NSCLC and highlighted the significant prognostic impact of suboptimal lymph node assessment. These results underscore the heterogeneity among R(un) patients and the need for precise resection assessment to improve outcomes.