*2.1. Study Population*

Formalin-fixed paraffin-embedded tumor tissues were obtained from 409 NSCLC patients who underwent curative surgical resection at the Department of Thoracic and Cardiovascular Surgery, Samsung Medical Center, Seoul, Korea, between August 1994 and May 2014. All samples were obtained from operative patients. Follow-up of patients for the detection of recurrence or death following curative resection was conducted by a nurse specialized in oncology as described previously [11]. The pathological stage of NSCLC was determined using the tumor/node/metastasis (TNM) system provided by the American Joint Committee on Cancer (AJCC) [12]. This study was conducted in accordance with the ethical principles stated in the Declaration of Helsinki and approved by the Institutional Review Board (IRB#: 2010-07-204) of the Samsung Medical Center. Written informed consent to use pathological specimens for research was obtained from all patients prior to surgery. All data are not publicly available due to privacy and ethical restriction.
