Intestinal LMNA::NTRK1-fused spindle cell neoplasm with S100 and CD34 coexpression: a new case

Recurrent fusions involving neurotrophin tyrosine receptor kinase (NTRK) genes have been increasingly recognised in spindle cell tumours of somatic soft tissues due to the widespread use of RNA-based sequencing techniques. This heterogeneous group of neoplasms is included as an emerging entity in the current WHO Classification of Soft Tissue and Bone Tumors. A subset of these tumours, associated with NTRK1 fusions, displays a distinctive phenotype in the form of monomorphic cytomorphology, patternless arrangement, perivascular and stromal hyalinisation, and CD34+/S100+/SOX10− immunoprofile. Gastrointestinal tract counterparts have been recently described with emphasis on distinction from KIT/PDGFRA/BRAF/RAS wild-type gastrointestinal stromal tumours (GIST). Here, we present a recently encountered intestinal spindle cell neoplasm harbouring an LMNA::NTRK1 gene fusion in a woman in her early 20s, which was initially thought to represent a GIST or a solitary fibrous tumour. Awareness of this emerging tumour type in the gastrointestinal tract is important due to treatment implications.