Routine multiplexed mutational analysis of colorectal cancers (CRCs): A single-institution experience.

Abstract

599 Background: Colorectal tumors harbor mutations in genes that play key roles in CRC carcinogenesis and that may enable prioritization of appropriate anti-cancer therapy. KRAS testing is part of standard of care testing prior to initiation of anti-epidermal growth factor receptor antibodies. Other mutations are emerging as significant drivers, but they are not yet part of routine screening. Methods: As part of Vanderbilt-Ingram Cancer Center’s Personalized Cancer Medicine Initiative, we developed a clinical algorithm to genotype patient’s colorectal tumors using a SNaPshot-based assay (multiplexed PCR, primer extension, and capillary electrophoresis) designed to detect 65 somatic mutations in 7 genes (KRAS, BRAF, AKT1, PIK3CA, SMAD4, PTEN, and NRAS) important in CRC carcinogenesis. Adult patients with metastatic CRC were consented for genotyping of tumor tissue. Mutational profiling was performed in Vanderbilt’s CLIA-certified Molecular Diagnostics Laboratory. Results were reported in the electronic medical record for clinical use. Results: Study enrolled from May 2012 to February 2014. SNaPshot results were available from 126 patients. 49 tumors (38.9%) were wildtype for all mutations tested. 58 (46.0%) tumors had a KRAS mutation, including one with two KRAS mutations; the most common was G12D (n=23), but two had a Q61H mutation and two had a K117N mutation, which are not included in some commercial KRAS tests. Ten (8.9%) tumors carried the V600E BRAF mutation. Nine (7.1%) tumors harbored a PIK3CA mutation. Three (2.4%) tumors had mutations in SMAD4. Four (3.2%) tumors had a NRAS mutation. One (0.8%) tumor had a PTEN mutation. Nine (7.1%) tumors harbored double mutations, the most common being KRAS and PIK3CA double mutations (N=6). 24 (19%) subjects subsequently were treated on clinical trial therapy, including 6 subjects on therapy based on the SNaPshot results. Not surprisingly, RAS results impacted use of anti-EGFR therapy. Conclusions: 61% of the tumors carried at least one mutation in the seven genes tested, suggesting that trials of tumor genotyping-based treatment assignment are feasible. Study was supported by Vanderbilt University Medical Center.