Simultaneous versus staged resection for synchronous colorectal cancer liver metastases: A population-based cohort study.

3612 Background: Simultaneous resection of colorectal cancer primary and liver metastases is not performed routinely due to concerns about safety. We hypothesized that simultaneous resection has steadily increased overtime and that the outcomes are similar. Methods: Population-based cohort study of patients undergoing resection for synchronous (resection of the primary colorectal cancer and liver metastases within six months) liver metastases from 2006-2015 by linking administrative datasets in Ontario, Canada. Outcomes: post-operative complications, length of hospital stay, and overall survival. Survival for the staged group was measured from the last surgical resection to death and estimated using Kaplan Meier and compared with the log-rank test. Cox proportional hazard models were used to calculate risks for death. We aimed to identify practice patterns, outcomes of simultaneous vs. staged resections for these patients. Results: Of 2,738 patients undergoing colorectal and liver resection for colorectal cancer, 1,168 were synchronous, of which, 442 underwent simultaneous resection. Rate of synchronous disease presentation increased on average by 3% per year (p = 0.02). Median length of stay was shorter (8 vs. 11 days, p < 0.001); rate of major liver resections were lower (17% vs. 65%, p < 0.001), and 90-day post-operative mortality was higher (6% vs. 1%) for simultaneous resections. Major postoperative complications were higher in the simultaneous group (28% vs. 23%, p = 0.067), mostly due to a higher reoperation rate (6% vs. 3%, p = 0.034). Median overall survival was worse with simultaneous resection (40 months, 95%CI 35-46 vs. 78 months, 95%CI 59-86). Risks factors for worse survival were comorbidities, rurality, right-sided primary and simultaneous resection. There is selection bias that favours survival in the staged group, as patients must have survived the first operation and have stable disease in order to undergo the second operation. Conclusions: Simultaneous resection is associated with worse postoperative outcomes. Considering selection bias, randomized studies would be necessary to determine the role of simultaneous.