Gastrointestinal stromal tumour with ETV6 rearrangement: a report of two cases and including a novel ETV6 and MOCS1/LRFN2 intergenic region fusion

Gastrointestinal stromal tumours (GISTs) are distinct mesenchymal tumours that arise from Cajal interstitial cells or their stem cell precursors. Most GISTs are driven by mutations in receptor tyrosine kinase genes, particularly KIT or PDGFRA. A smaller subset is associated with SDH deficiency, alterations in the RAS pathway (including NF1, BRAF and PIK3CA) or gene fusion events. Among these, the ETV6::NTRK3 fusion is one of the most recently described gene fusions in GISTs, with only eleven reported cases in the English literature.1 Here, we present two GIST cases: one harbouring the ETV6::NTRK3 fusion, and another representing an exceptionally unusual case characterised by diffuse chromogranin A (CgA) immunopositivity and a novel fusion involving the ETV6 and MOCS1/LRFN2 intergenic region. Furthermore, we aimed to explore the clinical, histopathological and molecular features of GISTs with ETV6 rearrangements to enhance our understanding of their biological behaviour.