ObjectiveThe necessity of mediastinal lymph node dissection (MLND) in segmentectomy remains uncertain as recent trials on intentional segmentectomy have made MLND mandatory. We conducted a retrospective study to evaluate the necessity of MLND in segmentectomy for patients with peripheral stage IA (≤2 cm) non-small-cell lung cancer (NSCLC). MethodsOf the 5,222 surgical cases for NSCLC from three institutions between 2010 and 2021, 1,457 patients met the JCOG0802 trial eligibility criteria. Initially, we analyzed 574 patients who underwent lobectomy with MLND to identify preoperative risk factors for cN0-pN2 occurrence (Cohort 1). Subsequently, we evaluated the relationship between these factors and the cumulative postoperative recurrence in 390 patients who underwent segmentectomy (Cohort 2). ResultsIn Cohort 1, risk factors for cN0-pN2 occurrence were consolidation-to-tumor ratio (CTR) =1.0 and maximum standardized uptake value (SUVmax) ≥2.0. When classifying patients into three groups (Group A without any factors, Group B with either factor, and Group C with both factors), the cN0-pN2 occurrence was significantly higher in Group C than in the other groups (0.9%, 3.4%, and 8.4%, respectively, P =0.005). When classifying patients in Cohort 2 using the classification identified in Cohort 1 (117, 131, and 142 were categorized into Group A, Group B, and Group C, respectively), the 5-year cumulative incidence of recurrence rate was significantly higher in Group C than in others (2.0%, 2.0%, and 15.9%, respectively, P <0.001). ConclusionsMLND is unlikely to be beneficial in intentional segmentectomy for patients with tumors showing CTR < 1.0 and SUVmax < 2.0.