title: Comparison of KRAS genotype: therascreen assay vs. LNA-mediated qPCR clamping assay.
abstract: BACKGROUND
  Kirsten rat sarcoma virus (KRAS) wild-type status determined using a locked nucleic acid (LNA)-mediated quantitative polymerase chain reaction (qPCR) clamping assay (LNA assay) predicted response to therapy in the CRYSTAL (Cetuximab Combined With Irinotecan in First-Line Therapy for Metastatic Colorectal Cancer) study. A companion KRAS diagnostic tool has been developed for routine clinical use (QIAGEN therascreen kit) (QIAGEN Manchester Ltd, Manchester, UK). We wanted to assess the concordance between the validated US Food and Drug Administration (FDA)-approved therascreen assay and the LNA assay in determining the KRAS status of a subset of patients enrolled in the CRYSTAL study.
  
  
  METHODS
  DNA extracted from paraffin-embedded tumor sections was tested for KRAS status using the therascreen assay. Efficacy data from the CRYSTAL study were assessed to determine if the overall survival (OS) hazard ratio for cetuximab in patients identified as having KRAS wild-type status using the therascreen assay was equivalent to that in patients identified as KRAS wild-type using the LNA assay. This was determined by assessing if the concordance between the therascreen assay and the LNA assay met the minimum threshold (prespecified as 0.8) to achieve a significant difference in the OS hazard ratio in favor of the cetuximab + FOLFIRI (5-fluorouracil, leucovorin [folinic acid], irinotecan) arm in the KRAS wild-type population as identified using the therascreen assay.
  
  
  RESULTS
  Of the 148 samples determined to be KRAS wild-type (therascreen assay), 141 (95.3%) samples were also KRAS wild-type (LNA assay) and 7 samples (4.7%) were KRAS mutant (LNA assay). The prespecified primary concordance measure p was 141/148 = 0.953 (95% confidence interval [CI], 0.905-0.981). The concordance was statistically significantly higher than the prespecified threshold of 0.8 for concordance between the therascreen assay and the LNA assay. Consistent with the concordance exceeding the prespecified threshold, the OS hazard ratio (cetuximab + FOLFIRI arm vs. FOLFIRI arm) in the KRAS wild-type population, determined by the therascreen assay, supported a significant benefit for cetuximab (ie, the 95% CI excluded 1) and was comparable to the OS hazard ratio observed in the CRYSTAL study KRAS wild-type population (LNA assay) even after adjustment for potentially confounding baseline variables.
  
  
  CONCLUSIONS
  These results support the utility of the therascreen assay for identifying patients who may benefit from cetuximab therapy for metastatic colorectal cancer.
authors: Eli Lilly and Co, Indianapolis, IN 46285, USA. changshao@lilly.com
authors: Shao-Chun
authors: SC
authors: Chang
authors: Jonathan
authors: J
authors: Denne
authors: Luping
authors: L
authors: Zhao
authors: Christine
authors: C
authors: Horak
authors: George
authors: G
authors: Green
authors: Shirin
authors: S
authors: Khambata-Ford
authors: Christopher
authors: C
authors: Bray
authors: Ilhan
authors: I
authors: Celik
authors: Eric
authors: E
authors: Van Cutsem
authors: Christopher
authors: C
authors: Harbison
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D002166:Camptothecin / Q000008:administration & dosage / Q000031:analogs & derivatives; D000068818:Cetuximab; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000401:mortality*; D004273:DNA, Neoplasm / Q000235:genetics; D005260:Female; D005472:Fluorouracil / Q000008:administration & dosage; D005500:Follow-Up Studies; D005838:Genotype; D006801:Humans; D000077146:Irinotecan; D002955:Leucovorin / Q000008:administration & dosage; D008297:Male; D008875:Middle Aged; D009154:Mutation / Q000235:genetics*; D009367:Neoplasm Staging; D009841:Oligonucleotides; D016133:Polymerase Chain Reaction; D011379:Prognosis; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D012189:Retrospective Studies; D015996:Survival Rate; D055815:Young Adult; D018631:ras Proteins / Q000235:genetics*
chemical_list: D061067:Antibodies, Monoclonal, Humanized; D004273:DNA, Neoplasm; C117307:KRAS protein, human; D009841:Oligonucleotides; D011518:Proto-Oncogene Proteins; C477371:locked nucleic acid; D000077146:Irinotecan; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D000068818:Cetuximab; D002955:Leucovorin; D005472:Fluorouracil; D002166:Camptothecin
keywords: Cetuximab; Colorectal cancer; EGFR inhibitors; KRAS; Mutation assay