Modern Outcome and Risk Analysis of Surgically Resected Occult N2 Non-Small Cell Lung Cancer

Background This study was performed to assess the incidence, survival, and risk factors associated with unsuspected pathologic N2 disease in patients with resectable clinical N0-1 non-small cell lung cancer. Methods Between January 2002 and December 2010, 1,821 patients with clinical N0-1 non-small cell lung cancer underwent pulmonary resection and mediastinal lymph node dissection. Clinical outcomes and risk factors for pathologic N2 disease were retrospectively analyzed for this cohort. Results Unsuspected pathologic N2 disease was identified in 196 patients (10.8%). The most common type of resection was lobectomy (81.6%). Adjuvant therapy was administered in 177 patients (90.3%). The median follow-up time was 28 months (range, 1 to 101 months). N2 involvement was single-station in 121 (66.8%) and multiple-station in 65 (33.2%). The 5-year overall and disease-free survival rates were 56.1% and 35.0%, respectively. The 5-year survival rates of single-station and multiple-station N2 were 66.6% and 36.4%, respectively ( p < 0.001). Adenocarcinoma, clinical N1, tumor size (>3 cm), and a right middle lobe tumor were identified as independent risk factors for unsuspected multiple-station N2 disease by multivariate analysis. Incidence of unsuspected multiple-station N2 disease in low-risk classes (aggregate score, 0 to ≤2) was only 5.5%. Conclusions The incidence of unsuspected N2 disease in our cohort was similar to that of previous reports. Survival outcomes were favorable for unsuspected single-station N2 disease but were poor for unsuspected multiple-station N2 disease. Clinical N0-1 non-small cell lung cancer patients with risk class of low score for unsuspected multiple-station N2 disease can be exempted from aggressive mediastinal staging.