A case of giant rectal gist successfully resected after neoadjuvant therapy with imatinib mesylate

Abstract

A 62-year-old woman was referred to our hospital for anal pain and constipation. Digital examination revealed an unmovable round and elastic hard tumor with a smooth surface in the anterior wall of the lower rectum. MRI showed that the tumor was 12 cm in diameter and was present in the lesser pelvic cavity. Colonoscopy revealed submucosal tumor with central ulceration. On the basis of findings from biopsy specimens, the tumor was diagnosed as a high-risk rectal gastrointestinal stromal tumor (GIST) with c-kit mutation of exon 11. We decided to administer neoadjuvant therapy with imatinib mesylate because the operative procedure had the risk of tumor cell dissemination due to rupture of tumor capsule and because the tumor had a c-kit mutation of exon 11. After 6 months of treatment, the tumor volume reduced to 40%. Abdominal-peritoneal resection with partial resection of the vaginal wall was performed without tumor perforation. Histological examination of the resected specimen revealed massive hyalinization and Ki-67 labeling index was significantly decreased. She was alive without recurrence after 14 months of operation followed by treatment with imatinib mesylate as adjuvant therapy.