Department of Gastrointestinal Surgery, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China. Department of Gastrointestinal Surgery, The Second Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China. Department of General Surgery, Beilun District People's Hospital, Ningbo, China. Department of Gastrointestinal Surgery, Zhejiang Provincial Hospital of Chinese Medicine, Hangzhou, China. Department of Hepatopancreatobiliary Surgery, Cancer Hospital of the University of Chinese Academy of Sciences, Hangzhou, China. Department of General Surgery, The Central Hospital of Lishui City, Lishui, China. Department of Gastrointestinal Surgery, The Second Affiliated Hospital of Wenzhou Medical College, Wenzhou, China. Department of General Surgery, The Sir Run Run Shaw Hospital, Medical School Zhejiang University, Hangzhou, China. Department of Gastrointestinal Surgery, Shandong Provincial Hospital, Jinan, China. Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China. Department of Gastrointestinal Surgery, Ningbo First Hospital, Ningbo, China. Department of Thyroid and Breast Surgery, The Affiliated People's Hospital of Ningbo University, Ningbo, China. Department of Epidemiology and Biostatistics, School of Public Health, Zhejiang University, Hangzhou, China.