Gang Xu1, Hua-Yu Yang1, Hai-Feng Xu2. 1. Department of Liver Surgery, Peking Union Medical College (PUMC) Hospital, PUMC & Chinese Academy of Medical Sciences, Beijing 100730, China. 2. Department of Liver Surgery, Peking Union Medical College (PUMC) Hospital, PUMC & Chinese Academy of Medical Sciences, Beijing 100730, China. Electronic address: xuhf781120@sina.com.