Low-grade NTRK-rearranged spindle cell neoplasm presenting as a colonic polyp and managed by polypectomy: a rare case report and literature review.

Background: NTRK-rearranged spindle cell neoplasms constitute a novel, heterogeneous group of mesenchymal neoplasms originally described predominantly in soft tissue locations. They are commonly characterized by co-expression of S100 and CD34 immunostains and presence of NTRK fusions. While exceedingly rare, there are increasing reports of this lesion involving the gastrointestinal tract, presenting predominantly as large masses of the stomach, small bowel and colorectum.

Case presentation: We present a case of a 37-year-old male who on colonoscopy was found to have a one cm polyp of the sigmoid colon which was removed by hot snare polypectomy. Histologic examination revealed haphazardly arranged bland spindle cells with diffuse CD34 and S100 co-expression. A targeted Next-Generation RNA Fusion Assay identified a TPR::NTRK1 fusion, confirming the diagnosis of low-grade NTRK-rearranged spindle cell neoplasm. The mucosal and deep margins were free of tumor. In contrast to the previously reported cases, the patient was managed with polypectomy and active surveillance, and remained disease-free at 14 months follow up.

Conclusion: This case contributes to the limited body of literature on gastrointestinal low-grade NTRK-rearranged spindle cell neoplasms and raises the possibility of endoscopic treatment consideration for carefully selected patients.