1. Department of Surgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Gangnam-Gu, Seoul 06351, Korea
2. Department of Surgery and Cancer Research Institute, Seoul National University College of Medicine, Chongno-Gu, Seoul 110-744, Korea
3. Department of Statistics, Seoul National University College of Natural Sciences, Gwanak-Gu, Seoul 08826, Korea
4. Department of Pathology, Seoul National University College of Medicine, Chongno-Gu, Seoul 110-744, Korea