title: Heterogeneous distribution of K-ras mutations in primary colon carcinomas: implications for EGFR-directed therapy.
abstract: OBJECTIVE
  K-ras mutations predict resistance against epidermal growth factor receptor (EGFR)-directed therapy of metastatic colorectal cancer (CRC). The purpose of this study was to analyze the distribution of K-ras mutations in primary tumors and corresponding sentinel lymph nodes (SLNs) from colon cancer patients.
  
  
  METHODS
  Tumor biopsies and SLNs from 158 patients with non-metastatic colon cancer were analyzed for K-ras mutations in codons 12 and 13 by a sensitive and quantitative peptide nucleic acid clamp PCR assay.
  
  
  RESULTS
  Analyses of single fresh-frozen tumor biopsies revealed K-ras mutations in 67 (42%) of the patients. Apparently low levels of K-ras mutations in 13 of the mutated primary tumors and the presence of K-ras mutations in SLNs from seven patients with a wild-type primary tumor biopsy suggested possible intratumoral heterogeneity for 20 of the patients. To confirm this hypothesis, we analyzed tissue sections from all available formalin-fixed, paraffin-embedded (FFPE) tumor blocks from these 20 patients. Ten of the patients had a mixture of tissue sections positive and tissue sections negative for K-ras mutations, two patients had K-ras mutations in all sections, and eight patients had no detectable K-ras mutations in tumor FFPE tissue blocks. Among these eight patients, five had K-ras mutations detected in SLNs. Thus, evidence supporting a heterogeneous distribution of K-ras mutations was obtained for 15 patients.
  
  
  CONCLUSIONS
  Heterogeneous distribution of K-ras codon 12 and 13 mutations within primary tumor, or between primary tumor and lymph node metastases, was demonstrated for 15 (20%) of 74 colon cancer patients having K-ras mutations. This may have implications for tissue sampling routines with regard to EGFR-directed therapy of CRC, both in adjuvant and metastatic settings.
authors.affiliation: Laboratory for Molecular Biology, Stavanger University Hospital, PO Box 8100, 4068, Stavanger, Norway.
authors.forename: Satu
authors.initials: S
authors.lastname: Oltedal
authors.forename: Ole Gunnar
authors.initials: OG
authors.lastname: Aasprong
authors.forename: Jannicke H
authors.initials: JH
authors.lastname: Møller
authors.forename: Hartwig
authors.initials: H
authors.lastname: Kørner
authors.forename: Bjørnar
authors.initials: B
authors.lastname: Gilje
authors.forename: Kjersti
authors.initials: K
authors.lastname: Tjensvoll
authors.forename: Elke M
authors.initials: EM
authors.lastname: Birkemeyer
authors.forename: Reino
authors.initials: R
authors.lastname: Heikkilä
authors.forename: Rune
authors.initials: R
authors.lastname: Smaaland
authors.forename: Oddmund
authors.initials: O
authors.lastname: Nordgård
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003110:Colonic Neoplasms / Q000235:genetics* / Q000473:pathology / Q000628:therapy; D066246:ErbB Receptors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D005557:Formaldehyde; D006801:Humans; D008875:Middle Aged; D058990:Molecular Targeted Therapy; D009154:Mutation / Q000235:genetics*; D016612:Paraffin Embedding; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D016707:Tissue Fixation; D018631:ras Proteins / Q000235:genetics*
chemical_list: C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D005557:Formaldehyde; D066246:ErbB Receptors; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins