389 – Anatomic Resection of Colorectal Liver Metastases Does Not Improve Outcomes over Non-Anatomic Resection Regardless of Ras Mutation Status

Introduction: Parenchymal-sparing (non-anatomic) resection has emerged as a safe and effective technique for resection of colorectal liver metastases (CRLM).More recently, RAS mutation has been identified as an important prognostic factor in patients undergoing CRLM resection.This calls into question the appropriateness of parenchymal-sparing techniques for this high-risk cohort.We compared outcomes of patients undergoing anatomic resections (AR) versus non-anatomic resections (NAR) in the context of RAS mutation status.Methods: Patients with known RAS mutation status who underwent AR or NAR for CRLM at a single institution during 2006-2016 were included.Patients with simultaneous AR and NAR were excluded, as were patients with two-stage hepatectomy, intraoperative ablation, or R2 resection.Differences in baseline characteristics between patients who underwent AR and NAR were adjusted using 1:1 propensity score matching.The variables included in the propensity score were: age, sex, ASA score, body mass index, bilateral vs. unilateral liver metastases, number of metastases, largest tumor diameter (as a continuous variable), neoadjuvant chemotherapy, extrahepatic disease, and repeated hepatectomy.Overall survival (OS), recurrencefree survival (RFS), and liver specific recurrence-free survival (L-RFS) were analyzed using log-rank statistics.Results: We identified 622 patients, of whom 338 (54%) underwent AR and 284 (46%) NAR.Patients who underwent AR had a higher median number of intrahepatic metastases (2 vs 1, p=0.002) and larger median tumor diameter (25 mm vs 16 mm, p<0.001) but were less likely to undergo a repeat hepatectomy (14% vs 24%, p=0.002).After matching, baseline characteristics were similar between patients with AR and NAR.In our initial cohort (before matching), there was higher OS with NAR than AR in the whole cohort (p=0.021), and a trend toward higher OS with NAR in the RAS mutant cohort (p=0.052),but there was no difference in OS in the wild-type RAS cohort (p=0.169).RFS was longer after NAR in patients with wild-type RAS (p=0.034), but RFS did not differ by resection type in the overall cohort or in patients with mutant RAS.There was no difference in L-RFS in any cohort prior to matching.After matching, no difference in OS, RFS, or L-RFS could be identified between AR and NAR in the overall cohort, in patients with wild-type RAS, or mutant RAS.There was no difference in the rate of R1 resection or recurrence at the resection margin between AR and NAR, before or after matching.Patients who underwent AR did have higher blood loss and longer length of stay.Conclusions: These data do not support the broad application of AR when it is not necessary to achieve an R0 resection, regardless of RAS mutation status.