Pediatric GIST

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Pediatric GIST

• Genetic progression mechanisms
• KIT/PDGFRA transforming roles

Katherine Janeway, MD
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Objectives

• To determine whether the incidence of KIT /
  PDGFRA mutations in a large group of pediatric
  patients is similar to that reported previously
  in smaller patient groups
• To correlate KIT / PDGFRA genotype with the
  activation status of KIT, PDGFRA and downstream
  signaling intermediates
• To define the chromosomal aberrations in
  pediatric GIST in relation to those seen in adult
  GIST

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Methods

• Patients
• 27 patients age less than 25 with confirmed GIST
• Subset of 15 patients had cryopreserved specimens
• KIT and PDGFRA mutation analysis
• KIT exons 9, 11, 13 and 17 and PDGFRA exons 12
  and 18 were PCR amplified and screened for
  mutations by high performance liquid
  chromatography
• The entire KIT coding sequence was PCR amplified
  from cDNA and sequenced using the ABI 3730 xl
  sequencer

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Methods

• SNP assay
• DNAs were isolated from cryopreserved tumor and
  analyzed using an Affymetrix 10K SNP array at the
  DFCI Microarray Core Facility
• Western blotting
• Whole cell lysates from cryopreserved tumors were
  separated by gel electrophoresis using 4 to 12
  Bis-Tris gels and blotted to nitrocellulose
  membranes. Immunostains were detected by enhanced
  chemiluminesence .

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KIT and PDGFRA genotyping

• Mutation analysis
• Three of 27 patients (11) with KIT or PDGFRA
  mutation
• KIT exon 11 homozygous deletion VV559-560 (17 yo)
• KIT exon 9 heterozygous AY502-503 tandem
  duplication (22 yo)
• PDGFRA exon 18 D842V point mutation (14 yo)
• Four patients with GISTs lacking mutations on
  genomic DNA sequencing also lacked KIT mutations
  upon sequencing of the entire coding region from
  cDNA

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Conclusions

• Most pediatric GISTs are KIT/PDGFRA - wildtype
• Our 27 cases plus 31 previously published
  genotyped cases
• 15 of pediatric GISTs harbor KIT or PDGFRA
  mutations
• Pediatric Adult
• KIT exon 11 5 66
• KIT exon 9 9 10
• PDGFRA 3 7

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Conclusions

• Mechanisms of genetic progression are
  significantly different in pediatric KIT-wildtype
  GISTs versus pediatric and adult KIT-mutant GISTs
• Biologically different tumors despite KIT
  expression and activation

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Conclusions

• Pediatric KIT-wildtype GISTs display KIT
  expression and activation at levels comparable
  with KIT-mutant pediatric and adult GISTs
• Mechanism is unclear
• Therapeutic inhibitors of KIT activation,
  particularly wildtype-KIT activation and
  inhibitors of signaling molecules downstream of
  KIT have the potential to be active in pediatric
  KIT-wildtype GIST

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Thanks!

• Brigham and Womens Hospital
• Jonathan Fletcher
• Bernadette Liegl
• Oregon Health Sciences University
• Mike Heinrich
• Chris Corless
• Childrens Hospital, Boston
• Antonio Perez-Atayde
• Harry Kozakewich

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