Transcriptome sequencing identifiesETV6–NTRK3as a gene fusion involved in GIST

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Gastrointestinal stromal tumours (GISTs) are the most common mesenchymal neoplasms of the gastrointestinal tract. The vast majority of GISTs are driven by oncogenic activation of KIT, PDGFRA or, less commonly, BRAF. Loss of succinate dehydrogenase complex activity has been identified in subsets ofKIT/PDGFRA/BRAF-mutation negative tumours, yet a significant fraction of GISTs are devoid of any of such alterations. To address the pathobiology of these 'quadruple-negative' GISTs, we sought to explore the possible involvement of fusion genes. To this end we performed transcriptome sequencing on fiveKIT/PDGFRA/BRAF-mutation negative, SDH-proficient tumours. Intriguingly, the analysis unveiled the presence of anETV6–NTRK3gene fusion. The screening by FISH of 26 additional cases, includingKIT/PDGFRA-mutated GISTs, failed to detect otherETV6rearrangements beside the index case. This was a 'quadruple-negative' GIST located in the rectum, an uncommon primary site for GIST development (˜4% of all GISTs). The fusion transcript identified encompasses exon 4 ofETV6and exon 14 ofNTRK3and therefore differs from the canonicalETV6–NTRK3chimera of infantile fibrosarcomas. However, it retains the ability to induce IRS1 phosphorylation, activate the IGF1R downstream signalling pathway and to be targeted by IGF1R and ALK inhibitors. Thus, theETV6–NTRK3fusion might identify a subset of GISTs with peculiar clinicopathological characteristics which could be eligible for such therapies. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

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