OBJECTIVE: The study aimed to evaluate the risk of unforeseen nodal upstaging (pN+) after pulmonary segmentectomy without intraoperative frozen section. METHODS: We conducted a retrospective analysis for consecutive patients who underwent segmentectomy for clinical stage IA1-2 non-small cell lung cancer (cIA1-2 NSCLC) in three centers between January 2017 and December 2022. A backward stepwise logistic regression analysis for variables with P <
0.1 in univariable analysis was performed to predict pN+. Kaplan-Meier analysis with log-rank test evaluated the discrepancy for overall (OS) and recurrence-free survivals (RFS). RESULTS: Among 478 patients included in the final analysis, 19 (4.0%) had pN+, including 10 (2.1%) pN1, 6 (1.3%) pN2, and 3 (0.6%) pN1+2. With a median follow-up of 23.5 months (interquartile range 12.6-39.0), patients with pN+ had poorer OS compared to those with pN0 (3-year OS: 70.2% vs. 89.7%, P = 0.002). However, there was no significant difference in RFS and recurrence. The maximum standardized uptake value (SUVmax) of tumor in positron emission tomography scan ≥ 4.5 (versus <
4.5) was the only independent factor for pN + (odds ratio 3.5). Patients with a SUVmax ≥ 4.5 had 7.3% pN+, which was associated with poorer OS and similar RFS and recurrence compared to pN0. In contrast, those with a SUVmax <
4.5 had 2.2% pN+, which had comparable recurrence and survival to pN0. CONCLUSION: Unforeseen nodal upstaging in segmentectomy for cIA1-2 NSCLC is low. Frozen section of lymph nodes may be necessary for lesions with high metabolic activity.