Clinicopathologic characteristics and gene expression analyses of non-KRAS 12/13, RAS-mutated metastatic colorectal cancer

Abstract

Background: KRAS mutations in codons 12 and 13 are present in ∼40% of all colorectal cancers (CRC). Activating mutations in codons 61 and 146 of KRAS and in codons 12, 13, and 61 of NRAS also occur but are less frequent. The clinicopathologic features and gene expression profiles of this latter subpopulation of RAS-mutant colorectal tumors have not yet been clearly defined but in general are treated similarly to those with KRAS 12 or 13 mutations.

Patients and methods: Records of patients with metastatic CRC (mCRC) treated at MD Anderson Cancer Center between December 2000 and August 2012 were reviewed for RAS (KRAS or NRAS) and BRAF mutation status, clinical characteristics, and survival outcomes. To study further with an independent cohort, data from The Cancer Genome Atlas were analyzed to define a gene expression signature for patients whose tumors feature these atypical RAS mutations and explore differences with KRAS 12/13-mutated colorectal tumors.

Results: Among the 484 patients reviewed, KRAS 12/13, KRAS 61/146, NRAS, and BRAF mutations were detected in 47.7%, 3.0%, 4.1%, and 7.4%, respectively, of patients who were tested for each of these aberrations. Lung metastases were more common in both the KRAS 12/13-mutated and atypical RAS-mutated cohorts relative to patients with RAS/BRAF wild-type tumors. Gene expression analyses revealed similar patterns regardless of the site of RAS mutation, and in silico functional algorithms predicted that KRAS and NRAS mutations in codons 12, 13, 61, and 146 alter the protein function and drive tumorgenesis.

Conclusions: Clinicopathologic characteristics, survival outcomes, functional impact, and gene expression profiling were similar between patients with KRAS 12/13 and those with NRAS or KRAS 61/146-mutated mCRC. These clinical and bioinformatic findings support the notion that colorectal tumors driven by these RAS mutations are phenotypically similar.

Keywords: KRAS; colorectal cancer; gene expression; next-generation sequencing; survival.

Figure 1.

Odds ratios for sites of distant metastases according to RAS mutation status. Atypical RAS-mutated tumors have similar metastatic patterns relative to KRAS 12/13-mutated tumors (A), whereas lung metastases are more common for tumors with KRAS 12/13 mutations (B) and with atypical RAS mutations (C) relative to RAS wild-type tumors.

Figure 2.

Overall survival of patients according to RAS mutational status and BRAF mutation (global P < 0.001). Hazard ratios listed are relative to wild-type and comparisons adjusted according to the Bonferroni method to account for multiple comparisons. WT, wild-type; OS, overall survival; mo, months; CI, confidence interval.

Figure 3.

Gene expression signature of KRAS 12/13-mutated versus KRAS/NRAS/BRAF wild-type tumors using RNA sequencing data from the CRC TCGA project. Genes in this expression signature constitute the rows in the heat map. The sample clustering of KRAS 12/13-mutated tumors with KRAS 61/146 plus NRAS 12/13/61-mutated tumors suggests that these two subsets of tumors behave similarly on the molecular level. WT, wild-type.