Use of a High-Throughput Genotyping Platform (OncoMap) for RAS Mutational Analysis to Predict Cetuximab Efficacy in Patients with Metastatic Colorectal Cancer

PURPOSE Cetuximab demonstrates improved efficacy outcomes in patients with metastatic colorectal cancer (mCRC) harboring wild-type KRAS exon 2. Resistance to cetuximab is mediated by activating less frequent mutations in the RAS genes beyond KRAS exon 2. We performed extended RAS Mutational analysis using a high-throughput genotyping platform (OncoMap) and evaluated extended RAS analysis for predicting cetuximab efficacy in patients harboring wild-type KRAS exon 2 tumors following Sanger sequencing. MATERIALS AND METHODS Extended RAS analysis was performed on 227 wild-type KRAS exon 2 mCRC patients who received cetuximab as salvage treatment using OncoMap ver. 4.0. Targeted genes included exon 2, exon 3, and exon 4, both in KRAS and NRAS, and included BRAF exon 15. We assessed efficacy by the new RAS mutation status. RESULTS The OncoMap detected 57 additional mutations (25.1%): 25 (11%) in KRAS exon 2 and 32 (14.1%) beyond KRAS exon 2. Survival differences were observed after dividing patients into the wild-type RAS group (n=170) and mutant RAS group (n=57) using OncoMap. Progression-free survival was 4.8 months versus 1.8 months (hazard ratio [HR], 0.44; 95% confidence interval [CI], 0.32 to 0.61), and overall survival was 11.9 months versus 8.4 months (HR, 0.65; 95% CI, 0.47 to 0.88). CONCLUSION Sanger sequencing is not sufficient for selecting candidates for cetuximab treatment. High-throughput extended RAS genotyping is a feasible approach for this purpose and identifies patients who might benefit from cetuximab treatment.