Embryologic Origin of the Primary Tumor and RAS Status Predict Survival after Resection of Colorectal Liver Metastases.

Background and objectives. In colorectal cancers, the embryologic origin of the primary tumor determines important molecular dissimilarities between right-sided (RS) and left-sided (LS) carcinomas. Although important prognostic differences have been revealed between RS- and LS-patients with resected colorectal liver metastases (CLMs), it is still unclear if this observation depends on the RAS mutational status. To refine the impact of primary tumor location (PTL) on the long-term outcomes of patients with resected CLMs, the rates of overall survival (OS), relapse-free survival (RFS) and survival after recurrence (SAR) were compared between RS- vs. LS-patients, according to their RAS status. Material and Methods. All patients with known RAS status, operated until December 2019, were selected from a prospectively maintained database, including all patients who underwent hepatectomy for histologically-proven CLMs. A log-rank test was used to compare survival rates between the RS- vs. LS-group, in RAS-mut and RAS-wt patients, respectively. A multivariate analysis was performed to assess if PTL was independently associated with OS, RFS or SAR. Results. In 53 patients with RAS-mut CLMs, the OS, RFS and SAR rates were not significantly different (p = 0.753, 0.945 and 0.973, respectively) between the RS and LS group. In 89 patients with RAS-wt CLMs, the OS and SAR rates were significantly higher (p = 0.007 and 0.001, respectively) in the LS group vs. RS group, while RFS rates were similar (p = 0.438). The multivariate analysis performed in RAS-wt patients revealed that RS primary (p = 0.009), extrahepatic metastases (p = 0.001), N-positive (p = 0.014), age higher than 65 (p = 0.002) and preoperative chemotherapy (p = 0.004) were independently associated with worse OS, while RS location (p < 0.001) and N-positive (p = 0.007) were independent prognostic factors for poor SAR. Conclusions. After resection of CLMs, PTL had no impact on long-term outcomes in RAS-mut patients, while in RAS-wt patients, the RS primary was independently associated with worse OS and SAR.