Primary NTRK-rearranged spindle cell sarcoma of the colon with ETV6-NTRK3 fusion

NTRK (neurotrophic receptor tyrosine kinase)-rearranged spindle cell tumours are rare sarcomas predominantly occurring in the extremities and trunk, with only rare gastrointestinal tract cases reported to date. A man in his late 30s presented with abdominal pain. Given the CT evidence of a large transmural tumour requiring radical resection irrespective of histological subtype, the multidisciplinary team proceeded directly to surgery without preoperative colonoscopy. Diagnosis was established through histopathology, immunohistochemistry (IHC) and next-generation sequencing (NGS). Right hemicolectomy revealed an 8 cm transmural spindle cell neoplasm with necrosis, vascular invasion and perineural infiltration. IHC showed diffuse strong CD31 positivity but negativity for CD117, DOG-1, S100 and smooth muscle markers. NGS identified an ETS Translocation Variant 6-Neurotrophic Tyrosine Receptor Kinase 3 gene (ETV6-NTRK3) fusion. Applying the American Joint Committee on Cancer (AJCC) 8th edition criteria for soft tissue sarcoma by analogy, the tumour was staged pT2N0M0 (stage IIIA, high grade). Adjuvant chemotherapy was discussed after multidisciplinary review of the complete (R0) resection but was declined by the patient for financial reasons; close surveillance was adopted. The patient remained recurrence-free at the 8-month follow-up. This case adds to the limited number of reported gastrointestinal NTRK-rearranged sarcomas and expands the anatomic and molecular spectrum of these tumours. CD31 expression was an unexpected observational finding in this case and requires independent validation before it can be considered a characteristic immunohistochemical feature. Molecular confirmation is essential for accurate diagnosis and for identifying patients who may be eligible for tropomyosin receptor kinase (TRK) inhibitor therapy.