A morphological mimic: An NTRK3-rearranged spindle cell neoplasm presenting as a groin mass.

Neurotrophic receptor tyrosine kinase (NTRK)-rearranged spindle cell neoplasms are a recently described group of soft tissue tumors. They commonly present as a painless mass on the extremities of children and young adults. They are characterized microscopically by a heterogeneous spectrum of infiltrative spindle cell proliferations, which can morphologically mimic several other spindle cell neoplasms. Their identification is vital, as they may be amenable to treatment with tyrosine kinase-targeted therapy. This case report describes a rare NTRK3-rearranged spindle cell neoplasm in the groin of a 29-year-old female and provides further clinical and morphological features of this entity.