Fig. 5: Immunophenotype of gastrointestinal mesenchymal tumors with NTRK rearrangements.

a A proliferation of bland spindle cells with palely eosinophilic cytoplasm and occasional perinuclear vacuoles may raise a morphological diagnosis of GIST (case 5). b TRK immunohistochemistry demonstrated diffuse and strong expression in this tumor with a TPM3–NTRK1 fusion. None of the tumors in this series expressed KIT (c) or DOG1 (d).