title: Companion-diagnostic testing limited to KRAS codons 12 and 13 misses 17% of potentially relevant RAS mutations in colorectal cancer.
abstract: BACKGROUND
  KRAS codons 12 and 13 mutations are commonly used to identify colorectal carcinoma (CRC) patients who are unlikely to benefit from anti-EGFR therapy. However, humans have four different homologous RAS proteins and no routine screening is performed for the other mutation sites. Non-screened mutations may still be present in a significant subset of patients without KRAS codon 12 and 13 mutations.
  
  
  METHODS
  We developed a LightCycler screening assay that encompasses codons 12, 13 and 61 of all RAS genes. Screen-positive specimens were characterized by Sanger sequencing. 130 CRC specimens were screened for all RAS genes. The results for KRAS codons 12 and 13 were compared with an FDA approved method (Qiagen).
  
  
  RESULTS
  Twenty-nine of 130 specimens (22.3%) were positive for KRAS codons 12 and 13, with 100% congruence with the Qiagen method. Six additional specimens were identified to have mutations. One mutation in HRAS codon 61, two in KRAS codon 61, and three in NRAS codon 61.
  
  
  CONCLUSIONS
  Limiting RAS testing to only KRAS codons 12 and 13 in companion diagnostic testing of CRC results in nearly 1/5 of patients with RAS mutations not being excluded from costly EGFR antagonist treatment, despite likely futility. Inclusion of all RAS genes in companion diagnostic screening is warranted.
authors.affiliation: Department of Laboratory Medicine and Pathology Mayo Clinic, Hilton 7, 200 1st Street SW, Rochester, MN 55905, USA.
authors.forename: Brian C
authors.initials: BC
authors.lastname: Netzel
authors.forename: Stefan K G
authors.initials: SK
authors.lastname: Grebe
mesh_terms: D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D002277:Carcinoma / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics; D003062:Codon; D015179:Colorectal Neoplasms / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics; D015870:Gene Expression; D005820:Genetic Testing / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D009154:Mutation; D010232:Paraffin; D016133:Polymerase Chain Reaction / Q000295:instrumentation / Q000379:methods*; D011518:Proto-Oncogene Proteins / Q000145:classification / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA; D016610:Tissue Embedding; D017211:Treatment Failure; D018631:ras Proteins / Q000145:classification / Q000235:genetics*
chemical_list: D000911:Antibodies, Monoclonal; D003062:Codon; C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D010232:Paraffin; C512478:EGFR protein, human; D066246:ErbB Receptors; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins
keywords: Anti-EGFR; Colorectal carcinoma; LightCycler; RAS