2.2. Patient selection

We collected data for patients with NSCLC defined by the International Statistical Classification of Diseases and Related Health Problems, 10th revision (ICD‐10) codes C340, C341, C342, C343, C348, who underwent surgery to remove one or more lung lobes because of malignant lung cancer between July 2010 and March 2015. We further selected NSCLC patients with TNM stage II‐IIIA based on the 7th edition of the TNM classification for lung cancer.⁸ We excluded patients aged ≤17 years at the time of lung surgery, patients who received more than one surgery, and patients with a diagnosis of distant metastasis (ICD‐10 codes C40, C41, C71, C72, C77, C787, C793, and C797) before surgery. To exclude patients who received neoadjuvant therapy and adjuvant radiotherapy, we excluded patients who received radiotherapy or chemotherapy before surgery or radiotherapy within 90 days after surgery. Patients who received adjuvant chemotherapy were defined as those who started a particular adjuvant chemotherapy regimen within 90 days after surgery, without starting drugs for any different regimens. We considered the first and last days of UFT or S‐1 use, and for VNR/CDDP treatment cycles, we counted the number of simultaneous injections of the two drugs within 270 days after surgery. We also considered other drugs that may be used to treat lung cancer (paclitaxel, gemcitabine, pemetrexed, docetaxel, vinblastine, vindesine, mitomycin, amrubicin, ifosfamide, cyclophosphamide, doxorubicin, etoposide, irinotecan, nogitecan, bevacizumab, gefitinib, erlotinib, afatinib, osimertinib, crizotinib, alectinib, ceritinib, nivolumab, and pembrolizumab).