1. Division of Thoracic Surgery, National Cancer Center Hospital East , 6-5-1 Kashiwanoha, Kashiwa, Chiba 277-8577 , Japan
2. Department of Surgery II, Faculty of Medicine , 2-2-2 Iida-Nishi, Yamagatashi, Yamagata 990-9585 , Japan
3. JCOG Data Center/Operations Office, National Cancer Center Hospital , 5-1-1 Tsukiji, Chuoku, Tokyo, 104-0045 , Japan
4. Division of Thoracic Surgery, National Cancer Center Hospital , 5-1-1 Tsukiji, Chuoku, Tokyo, 104-0045 , Japan