A case of quadruple wild-type gastrointestinal stromal tumor with CDC42BPB::NTRK3 fusion and abundant lymphoid infiltration.

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. The most common mutations in GISTs are those in receptor tyrosine kinase (KIT) and platelet-derived growth factor receptor alpha (PDGFRA). GISTs without KIT or PDGFRA mutations are defined as wild-type (WT) GISTs. The molecular changes, prognosis, and treatments of WT GISTs remain uncertain. Among WT GISTs, neurotrophic tyrosine receptor kinase (NTRK) fusions have rarely been reported. We report a case of quadruple wild-type GIST harboring a novel CDC42BPB::NTRK3 fusion. In this study, we described a 66-year-old male patient with intrajejunal lesion. This case showed massive lymphocytic and plasma cell infiltration, which caused diagnostic difficulties in morphology. CDC42BPB::NTRK3 fusion was detected via next-generation sequencing (NGS), and this finding was confirmed by fluorescence in situ hybridization (FISH), which revealed NTRK3 breakage. However, the expression of the Trk protein in tumor tissue was not detected by immunohistochemistry (IHC). This finding expands the genetic spectrum of NTRK rearrangements in GISTs.