Association of RAS Mutation Location and Oncologic Outcomes After Resection of Colorectal Liver Metastases.

Background: RAS mutations are prognostic for patients with metastatic colorectal cancer (mCRC). We investigated clinical, pathologic, and survival differences based on RAS exon for patients with colorectal liver metastases (CRLM).

Methods: This retrospective, single-center study included patients with R0/R1 resection of CRLM from 1992 to 2016. Patients with unresected extrahepatic disease or liver-first resection were excluded. Overall survival (OS) and recurrence-free survival were assessed and stratified by mutation status and location. Fisher's exact test, Wilcoxon rank-sum test, and log-rank test were used, where appropriate.

Results: A total of 938 mCRC patients were identified with median age of 57 (range 19-91). Of the 445 patients with KRAS mutations, 407 (91%) had a mutation in exon 2, 14 (3%) exon 3, and 24 (5%) exon 4. Median OS was 71.4 months (95% confidence interval [CI] 66.1-76.5). Patients with KRAS mutations had worse OS compared with KRAS wild-type patients (median 55.5 vs. 91.3 months, p < 0.001). While there was no significant difference in OS based on the exon mutated (p = 0.12), 5-year OS was higher for patients with exon 4 mutations [68.8% (95% CI 0.45-0.84)] compared with those with mutations in exon 2 [45.7% (95% CI 0.40-0.51)] or exon 3 [39.1% (95% CI: 0.11-0.68)]. Patients with NRAS mutant tumors also had worse OS compared with NRAS wild-type patients (median 50.9 vs. 73.3 months, p = 0.03).

Conclusions: NRAS and KRAS exon 3/4 mutations are present in a minority of mCRC patients. Patients with exon 4 mutant tumors may have a more favorable prognosis, although the difference in oncologic outcomes based on mutated exon appears to be smaller than previously reported.