*2.1. Inclusion Criteria*

From 1 January 2006 to 31 December 2014, 748 patients with lung cancer underwent surgical resection with mediastinal lymph node dissection or sampling at China Medical University Hospital. The tumor-node-metastasis (TNM) staging system was reclassified according to the eighth edition of the AJCC staging system. A total of 77 (10.3%) patients with stage IIIA-N2 NSCLC who underwent surgical resection with curative intent were enrolled in the study. Smoking status was classified as ever (including current and former smoker) or never smoker. Family history of cancer was defined as any first-degree relative diagnosed with any form of cancer. The preoperative staging workup included complete blood count, serum biochemistry, carcinoembryonic antigen (CEA), chest radiography, chest computed tomography (CT) scan, bronchoscopy, and nuclear medicine exam. Patients with positive surgical tumor margin and incomplete medical record were excluded. There were weekly multidisciplinary lung cancer meetings where thoracic radiologists, radiation oncologist, surgeons, and pulmonologists from the China Medical University Hospital jointly reviewed and discussed the management plan of patients with lung cancer.

### *2.2. Surgical Technique*

Only patients having the Eastern Cooperative Oncology Group (ECOG) performance of 0 or 1 were considered as surgical candidates, and all surgery was performed with curative intent. All patients underwent surgery either with preoperatively clinical N2 disease or unexpectedly during surgery. Tumor location was analyzed as dichotomous variables (lower versus upper or middle lobes; peripheral

(outer one-third of lung field) versus central (inner two-thirds of lung fields)). Induction therapy was defined as preoperative chemotherapy and/or radiotherapy. Adjuvant therapy was defined as treatment with either chemotherapy, radiotherapy, or a combination of both after surgical resection. The type of surgery included standard (pneumonectomy, bilobectomy, or lobectomy) and limited resection (wedge resection or segmentectomy). Mediastinal lymph node dissection or sampling with a minimum of three different stations was performed according to the surgeon's experience, and all resected lymph nodes were labeled separately. All pulmonary resections were performed either through open thoracotomy or video-assisted thoracoscopic surgery (VATS).
