We tested the activity of avapritinib, a potent and highly selective inhibitor of mutated KIT and PDGFRA, in three patient-derived xenograft (PDX) GIST models carrying different <i>KIT</i> mutations, with differential sensitivity to standard TKI.<b>Experimental Design:</b> NMRI <i>nu/nu</i> mice (<i>n</i> = 93) were transplanted with human GIST xenografts with <i>KIT</i> exon 11+17 (UZLX-GIST9 <i>
Our results suggest that KIT/PDGFRA mutation is a very common early event in GIST development, that tumour size does not reliably predict the presence of mutation, and that one or more subsequent mutations are required for clinical manifestation.
This homogeneity suggests that the molecular pathogenesis of a GIST results from expansion of a clone that has acquired an activating mutation in KIT without the extreme genetic instability found in the common epithelial cancers.
The introduction of imatinib, an orally administered inhibitor of the KIT receptor tyrosine kinase, is prompting revision of the management algorithms that have traditionally guided the treatment of gastrointestinal stromal tumor (GIST).
Activating mutations of KIT were found in 14 (50%) GISTs, the majority being within exon 11 (n=11; 39.2%), and the other comprised exon 9 AY 502-503 duplications (n=2; 7.2%) and exon 17 Lys --> Aln822 missense mutations (n=1; 3.6%).
In particular, the responsiveness of GISTs to treatment with the kinase inhibitor imatinib varies substantially depending on the exonic location of the KIT or PDGFRA mutation.
Ripretinib shows efficacy in preclinical cancer models, and preliminary clinical data provide proof-of-concept that ripretinib inhibits a wide range of KIT mutants in patients with drug-resistant GISTs.
Additionally, even if the KIT-mutated GISTs alone were considered, a significantly higher expression of PDGFRA could be observed in gastric than in intestinal tumors.
There is growing evidence of phenotype-genotype (KIT, platelet-derived growth factor receptor-alpha, succinate dehydrogenase or other driver gene mutation) and genotype-therapeutic (sensitivity to imatinib) correlations in GIST.
Most KIT mutations occur in untreated GISTs in the juxtamembrane exon 11 and only rarely in the kinase domain, whereas in imatinib-treated patients secondary mutations are frequent in exons encoding for the ATP/imatinib binding pocket or the kinase activation loop.
We evaluated GISTs from three females with incomplete Carney triad for KIT and PDGFRA mutations and studied the DNA by comparative genomic hybridization (CGH).
Molecular analysis was available for 29/46 patients with a second tumor: wild-type GISTs (n. 5), exon 11 (n. 16), exon 13 (n. 1), exon 9 (n. 1) KIT mutations, exon 14 PDGFR-α mutation (n. 2) and exon 18 PDGFR-α mutation (n. 4).