Giant Gastrointestinal Stromal Tumor of the Rectum Harboring an Exon-9 KIT Mutation

Abstract

A 54-year-old female patient was admitted to our hospital with a history of feeling a swelling at the vaginal introitus. Colonoscopy showed a submucosal tumor measuring 60 mm in diameter in the lower rectum, above the anal canal. Aspiration biopsy was positive for c-kit and CD34, and the tumor was diagnosed as a gastrointestinal stromal tumor of the rectum. Computed tomography revealed a tumor measuring 10 cm in diameter between the vagina and the lower rectum. There was no evidence of either lymph node or distant metastasis. Although preoperative imatinib mesylate therapy was considered, surgical resection was selected, because immunohistochemical examination of a biopsy specimen revealed an Exon-9 KIT mutation. Therefore, abdominoperineal resection with resection of the posterior wall of the vagina was performed. The defect in the vaginal wall was reconstructed using a gluteal fold flap by plastic surgeons. The patient did not receive adjuvant therapy, but remains alive 18 months after the operation with no evidence of recurrence.