Despite the recent development of radiologic mediastinal staging modality, unexpected mediastinal lymph node metastasis still occurs. Preoperative accurate nodal staging is important to determine the optimal treatment. Therefore, this study aimed to identify predictors of unexpected N2 disease in non–small-cell lung cancer (NSCLC).

Data from a multicenter database of 2802 patients with clinical T1-2N0-1M0 NSCLC who underwent anatomical segmentectomy or lobectomy were retrospectively analyzed. Unexpected N2 disease was defined as pathologic N2 disease with clinical N0 or N1. The predictive criteria of unexpected N2 disease were established on the basis of the multivariable analysis results of a derivation cohort of 2019 patients, and the criteria were further tested in a validation cohort of 783 patients.

In multivariable analyses, maximum standardized uptake value (SUVmax) of the primary tumor on 18-fluoro-2-deoxyglucose positron emission tomography/computed tomography (odds ratio, 1.072; 95% confidence interval, 1.018−1.129; P = .008) and clinical N1 (vs. clinical N0) disease (odds ratio, 5.40; 95% confidence interval, 1.829−15.94; P = .002) were independent predictors of unexpected N2 disease. The predictive criteria of unexpected N2 disease was defined as tumors with SUVmax of ≥ 3.1, determined by receiver operating characteristic curves, and clinical N1 disease. This criterion showed diagnostic accuracy of 90.6% (sensitivity 32.0%, specificity 94.5%) in the derivation cohort and 91.3% (sensitivity 32.6%, specificity 94.7%) in the validation cohort.

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