ObjectiveTo evaluate the safety and efficacy of simultaneous resection for initially resectable rectal cancer with synchronous liver metastases.MethodsA retrospective analysis was conducted on 305 patients with initially resectable rectal cancer with synchronous liver metastases. These patients were diagnosed at Zhongshan Hospital, Fudan University from January 2016 to June 2020. Among them, 191 underwent simultaneous rectum and liver resection and 114 underwent staged resection. Propensity score matching (PSM) was performed at a 1∶1 ratio. Clinical data were compared and Kaplan-Meier survival curves were plotted.ResultsAfter PSM, 85 patients were included in each group. General data showed no significant differences. Except for liver metastasis resection method, no statistical differences were found in primary tumor surgery approach, intraoperative blood loss, intraoperative complications, time to first flatus and defecation, 30-day mortality, and postoperative hospital stay between the simultaneous resection group and the staged resection group. The overall complication rate was higher in the simultaneous resection group (48.2% vs 29.4%, P=0.04). Specifically, the grade Ⅱ complications were significantly higher (29.4% vs 14.1%, P=0.016), but there's no differences in severe complications (grade Ⅲ-Ⅴ). No statistically differences were observed in median progressionfree survival (HR=0.70, 95%CI 0.50-0.97, P=0.103) and 5-year overall survival (HR=0.95, 95%CI 0.63-1.44, P=0.259).ConclusionsSimultaneous resection demonstrates comparable safety and efficacy to staged resection for initially resectable rectal cancer with synchronous liver metastases.