Prognostic value of RAS, BRAF, and PIK3CA mutations in early-stage colorectal cancer.

Abstract

594 Background: Activating mutations in the KRAS, BRAF and PIK3CA oncogenes deregulate growth-factor pathways and promote metastasis in colorectal cancer (CRC). The prognostic value of these mutations has been reported with conflicting results in early CRC. We evaluated RAS, BRAF, and PIK3CA mutations as prognostic biomarkers in early stage (stage I-III) colorectal cancer (CRC) patients. Methods: Tumor samples collected from 302 early stage CRC patients diagnosed between 1998 and 2010 were analyzed as part of a multi-institutional observational study. Targeted exome sequencing was performed using the Illumina NGS platform with 50-100X coverage of mutations. The BWA/GATK pipeline was used to identify variants and indels. Matched normal samples were not available for comparison to identify somatic mutations, therefore 1000 Genomes was used to filter normal variants. Variants identified in 1000 Genomes with an MAF <0.01 were filtered. Overall survival data was collected via retrospective chart review. Extended RAS, BRAF V600E, and PIK3CA (exon 9 and 20) mutations were evaluated. The log-rank test was used to compare survival distributions. Results: 302 patients were eligible for analysis (53 stage I, 125 stage II, 124 stage III). 109 patients had RAS mutations (KRAS or NRAS), 41 patients had BRAF mutations, and 29 patients had PIK3CA mutations. Of the 247 patients with microsatellite stability (MSS) 98 were RAS mutant, 10 were BRAF mutant, and 19 were PIK3CA mutant. Of the 55 patients with microsatellite instability high (MSI-H) 11 were RAS mutant, 31 were BRAF mutant, and 10 were PIK3CA mutant. BRAF mutation was prognostic for decreased OS (p= 0.0245), particularly in patients with MSS tumors (p=0.0141). RAS and PIK3CA mutations did not have prognostic value for OS (p =0.72 and 0.23 respectively). Conclusions: In early stage colorectal cancer, we confirmed BRAF mutation is prognostic for OS particularly in MSS patients. RAS and PIK3CA mutations did not confer prognostic value.