Abstract
A 76-year-old woman was admitted to the hospital because of anal discomfort and bleeding at defecation. An elastic hard tumor was palpable near the anal margin. Pelvic CT and magnetic resonance imaging scans showed a submucosal tumor about 2cm in diameter with clear margin in the ventral aspect of rectum. Colonoscopy showed a submucosal tumor with ulceration placed oral side of the anal margin, and the tumor was diagnosed as low grade malignant rectal gastrointestinal stromal tumor (GIST) by biopsy. No invasive sign was found in various preoperative examinations. Local resection was performed through the anus. The removed tumor was 1.8cm in longer diameter, and showed central necrosis accompanied with bleeding on section. The positive staining for c-kit and CD34 was confirmed by immunohistochemical staining, and the proliferation rate was high (60/50HPF). The final pathological diagnosis was rectal GIST with high grade malignancy. A large part of rectal submucosal tumors smaller than 2cm in diameter are followed up without treating in clinical cases. However, careful and adequate diagnosis is required because of high malignant potential in some tumors.
