Taken together, our study suggests a model in which overexpression of wild-type PDGFRA associated with NF1 deficiency leads to aberrant activation of downstream RAS signaling and thus contributes importantly to MPNST development-a prediction supported by the ability of the kinase inhibitor sunitinib alone and in combination with the MEK inhibitor trametinib to retard MPNST progression in transgenic fish overexpressing the wild-type receptor.
The molecular biology of these GIST, originally defined as KIT/PDGFRA wild-type (WT), is complex due to the existence of different subgroups with distinct molecular hallmarks, including defects in the succinate dehydrogenase (SDH) complex and mutations of neurofibromatosis type 1 (NF1), BRAF, or KRAS genes (RAS-pathway or RAS-P).In this extremely heterogeneous landscape, the clinical profile and molecular abnormalities of the small subgroup of WT GIST suitably referred to as quadruple wild-type GIST (quadrupleWT or KITWT/PDGFRAWT/SDHWT/RAS-PWT) remains undefined.
In contrast to sporadic GISTs characterized by frequent allelic losses of 1p, 14q and 22q and mutations of KIT or PDGFRA gene with the activation of the downstream RAS-MAPK pathway, the molecular pathogenetic mechanisms of NF-1-related GISTs (NF-1 GISTs) remain unclear.
Concomitant amplifications of HGF, MET, and PDGFRA genes were also revealed in MPNSTs, suggesting the putative role of p70S6K pathway in NF1 tumor progression.
NF-1-associated GISTs are usually wild type for c-KIT and platelet-derived growth factor receptor-alpha (PDGFR-alpha) mutations and harbor a different oncogenic molecular mechanism.
Multifocal gastrointestinal stromal tumors (GISTs) are observed in patients with germline KIT or PDGFRA mutations, and in those with neurofibromatosis 1.
GISTs in patients with neurofibromatosis type 1 appear to lack the KIT and PDGFRA mutations characteristic of GISTs and may have a different pathogenetic mechanism.
We demonstrate that (i) the NF1-related GISTs do not have KIT or PDGFRA mutations, (ii) the molecular event underlying GIST development in this patient group is a somatic inactivation of the wild-type NF1 allele in the tumor and (iii) inactivation of neurofibromin is an alternate mechanism to (hyper) activate the MAP-kinase pathway, while the JAK-STAT3 and PI3K-AKT pathways are less activated in NF1-related GIST compared with sporadic GISTs.
Multiple gastrointestinal stromal tumors typically occur in familial form associated with KIT receptor tyrosine kinase or platelet-derived growth factor receptor-alpha (PDGFRA) germline mutations, but may also develop in the setting of type 1 neurofibromatosis.