title: Intratumoral heterogeneity of KRAS mutation is rare in non-small-cell lung cancer.
abstract: BACKGROUND
  Several lines of evidence indicate that mutational activation of KRAS is an early event in the carcinogenesis of non-small cell lung cancer (NSCLC). Nonetheless, previous studies report high frequencies of divergent KRAS mutational status between primary NSCLC and corresponding metastases. This suggests heterogeneity of the primary tumor in respect to its KRAS status. We therefore aimed to examine the frequency and the extent of such intratumoral heterogeneity.
  
  
  METHODS
  40 NSCLC were examined for intratumoral heterogeneity of KRAS mutation (20 adenocarcinomas, 10 squamous cell carcinomas and 10 large cell carcinomas). Three to eight different tumor areas were analyzed for KRAS mutation and up to four corresponding lymph node metastases were included for analysis in nineteen cases. A combination of different methods for screening of heterogeneity and its validation were used including direct sequencing, laser-capture microdissection for tumor cell enrichment and the very sensitive ARMS/S method.
  
  
  RESULTS
  Mutations of KRAS were found in 13/30 adenocarcinomas and large cell carcinomas. No mutations were detected in 10 squamous cell carcinomas. Four cases showed heterogeneous KRAS results by direct sequencing. More sensitive methods for KRAS mutation analysis revealed false negative results due to admixture of non-neoplastic cells in all of these samples. Intratumoral heterogeneity of KRAS mutational status was therefore confirmed in none of the analyzed cases. In addition, identical KRAS mutations were present in the primary tumor and the corresponding lymph node metastases in 19 cases examined.
  
  
  CONCLUSIONS
  Intratumoral heterogeneity of KRAS mutational status is rare in NSCLC but highly sensitive tools are required to reliably identify these mutations. This finding is in line with the hypothesis that oncogenic activation of KRAS is an early event and a bona fide "driver mutation" in NSCLC. Furthermore, future therapies targeting KRAS will not be limited by intratumoral heterogeneity.
authors.affiliation: Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Winfried H
authors.initials: WH
authors.lastname: Alsdorf
authors.forename: Till S
authors.initials: TS
authors.lastname: Clauditz
authors.forename: Tobias
authors.initials: T
authors.lastname: Hoenig
authors.forename: Alexander
authors.initials: A
authors.lastname: Quaas
authors.forename: Hüseyin
authors.initials: H
authors.lastname: Sirma
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Koenig
authors.forename: Jakob
authors.initials: J
authors.lastname: Izbicki
authors.forename: Guido
authors.initials: G
authors.lastname: Sauter
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Marx
authors.forename: Tobias J
authors.initials: TJ
authors.lastname: Grob
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000556:secondary; D011905:Genes, ras; D014644:Genetic Variation; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology; D008207:Lymphatic Metastasis / Q000235:genetics*; D009154:Mutation; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D017422:Sequence Analysis, DNA; D018631:ras Proteins / Q000235:genetics*
chemical_list: C117307:KRAS protein, human; D011518:Proto-Oncogene Proteins; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins