Simultaneous Versus Staged Resection for Initially Resectable Synchronous Rectal Cancer Liver-limited Metastasis

Inclusion Criteria: * age\>=18 and \<= 75 years * resectable primary rectal tumor * remnant liver volume \>= 60% * without other organ metastasis or peritoneum metastasis * without contradiction of cardiac and pulmonary diseases * American Society of Anesthesiologists (ASA) class I - II * Histologically proved rectal adenocarcinoma Exclusion Criteria: * age \> 75 years * unresectable primary rectal tumor * remnant liver volume \< 60% * with other organ metastasis or peritoneum metastasis * with contradiction of cardiac and pulmonary diseases * Tumors assessed as clinical complete response after preoperative radio- or chemoradiotherapy * Signs of acute intestinal obstruction, bleeding or perforation needing emergency surgery * Multiple colorectal tumors or other schedules needing for synchronous colon surgery * Co-existent inflammatory bowel disease * Pregnancy or lactation * Patients received treatment other than preoperative radio- or chemoradiotherapy