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Pediatric GIST

Pediatric GIST. Genetic progression mechanisms KIT/PDGFRA transforming roles. Katherine Janeway, MD. 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

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Pediatric GIST

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  1. Pediatric GIST Genetic progression mechanisms KIT/PDGFRA transforming roles Katherine Janeway, MD

  2. 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

  3. 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

  4. 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 .

  5. 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

  6. 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%

  7. 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

  8. 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

  9. Thanks! • Brigham and Women’s Hospital • Jonathan Fletcher • Bernadette Liegl • Oregon Health Sciences University • Mike Heinrich • Chris Corless • Children’s Hospital, Boston • Antonio Perez-Atayde • Harry Kozakewich Big Papi

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