Incidental Discovery of a Sigmoid Colon Gastrointestinal Stromal Tumor Mimicking Colitis: A Case Report.

Gastrointestinal stromal tumors (GISTs) of the colon are extremely rare and often present diagnostic challenges due to overlapping features with inflammatory or other neoplastic conditions. We report the case of a 43-year-old female initially referred for evaluation of presumed colitis who was found on colonoscopy to have a sigmoid mass. Initial biopsies showed inflammation without malignancy, but subsequent imaging and pathology confirmed a GIST. After multidisciplinary evaluation, she underwent an uncomplicated robotic-assisted partial colectomy. Final pathology confirmed a 2.2 × 1.9 × 0.6 cm low-mitotic index GIST positive for CD117 and DOG-1, with no residual disease. Postoperative recovery was favorable; adjuvant management is ongoing. This case highlights the importance of maintaining a broad differential for colonic masses and demonstrates how early multidisciplinary intervention can guide optimal surgical and oncologic care, even in atypical GIST presentations.