Gastric Spindle Cell Neoplasm With LMNA::NTRK1 Fusion: A Rare Mimic of Wild‐Type GIST

Abstract

Neurotrophic tyrosine receptor kinase‐rearranged spindle cell neoplasms (NTRK‐SCNs) are rare mesenchymal tumours defined by oncogenic rearrangements involving NTRK genes. NTRK fusions are exceedingly rare in the gastrointestinal tract and can closely resemble wild‐type gastrointestinal stromal tumours (GISTs), posing a diagnostic challenge in the absence of molecular testing. We report a case of a 36‐year‐old woman with a distal gastric mass initially suspected to be a GIST. Surgical resection revealed a spindle cell tumour with low mitotic activity and perivascular hyalinisation. Immunohistochemistry demonstrated expression of CD34, S100 and pan‐TRK and was negative for KIT/CD117 and DOG1. Molecular testing confirmed an LMNA::NTRK1 fusion, consistent with NTRK‐SCN. This case highlights the importance of considering NTRK‐SCN in KIT/DOG1‐negative gastric spindle cell tumours.