title: KRAS and BRAF mutations predict primary resistance to imatinib in gastrointestinal stromal tumors.
abstract: OBJECTIVE
  Gastrointestinal stromal tumors (GIST) are characterized by gain-of-function mutations in KIT/PDGFRA genes leading to a constitutive receptor activation which is well counteracted by imatinib. However, cases in which imatinib as first-line treatment has no effects are reported (primary resistance). Our purpose is to investigate alterations in downstream effectors, not reported so far in mutated GIST, possibly explaining the primary resistance to targeted treatments.
  
  
  METHODS
  Two independent naive GIST cohorts have been analyzed for KIT, PDGFRA, KRAS, and BRAF mutations by direct sequencing. Cell lines expressing a constitutively activated and imatinib-responding KIT, alone or in combination with activated KRAS and BRAF, were produced and treated with imatinib. KIT receptor and its downstream effectors were analyzed by direct Western blotting.
  
  
  RESULTS
  In naive GISTs carrying activating mutations in KIT or PDGFRA a concomitant activating mutation was detected in KRAS (5%) or BRAF (about 2%) genes. In vitro experiments showed that imatinib was able to switch off the mutated receptor KIT but not the downstream signaling triggered by RAS-RAF effectors.
  
  
  CONCLUSIONS
  These data suggest the activation of mitogen-activated protein kinase pathway as a possible novel mechanism of primary resistance to imatinib in GISTs and could explain the survival curves obtained from several clinical studies where 2% to 4% of patients with GIST treated with imatinib, despite carrying KIT-sensitive mutations, do not respond to the treatment.
authors.affiliation: Department of Experimental Oncology and Molecular Medicine, Istituto Nazionale dei Tumori IRCCS Foundation, Milan, Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Miranda
authors.forename: Martina
authors.initials: M
authors.lastname: Nucifora
authors.forename: Francesca
authors.initials: F
authors.lastname: Molinari
authors.forename: Elena
authors.initials: E
authors.lastname: Conca
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: Anania
authors.forename: Andrea
authors.initials: A
authors.lastname: Bordoni
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Saletti
authors.forename: Luca
authors.initials: L
authors.lastname: Mazzucchelli
authors.forename: Silvana
authors.initials: S
authors.lastname: Pilotti
authors.forename: Marco A
authors.initials: MA
authors.lastname: Pierotti
authors.forename: Elena
authors.initials: E
authors.lastname: Tamborini
authors.forename: Angela
authors.initials: A
authors.lastname: Greco
authors.forename: Milo
authors.initials: M
authors.lastname: Frattini
mesh_terms: D016475:3T3 Cells; D000368:Aged; D000818:Animals; D001549:Benzamides; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000188:drug therapy* / Q000235:genetics*; D046152:Gastrointestinal Stromal Tumors / Q000188:drug therapy* / Q000235:genetics*; D011905:Genes, ras; D057809:HEK293 Cells; D006801:Humans; D000068877:Imatinib Mesylate; D020935:MAP Kinase Signaling System / Q000235:genetics; D008297:Male; D051379:Mice; D008875:Middle Aged; D009154:Mutation; D010879:Piperazines / Q000627:therapeutic use*; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D011743:Pyrimidines / Q000627:therapeutic use*
chemical_list: D001549:Benzamides; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D000068877:Imatinib Mesylate; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf