Local Excision with Adjuvant Imatinib Therapy for Anorectal Gastrointestinal Stromal Tumors

Rectal gastrointestinal stromal tumors (GISTs) are uncommon, and the role of local excision versus a more extensive resection after the advent of effective targeted chemotherapy with imatinib is not known. Our aim is to present two cases of large anorectal GIST treated with local excision through a new anterolateral trans-sphincteric approach followed by adjuvant therapy with imatinib. Two patients (both males, 68 and 63 years old) presented at our institution with anorectal GIST in the period October-November 2010. Their medical records, pathology results, and imaging studies were retrospectively reviewed. Both patients presented with an anterior perianal mass. Imaging studies were characteristic of GIST originating in the lower rectum, circumscribed by a pseudocapsule, and protruding into the ischiorectal fossa. Both patients underwent local excision via an anterolateral trans-sphincteric approach. Both tumors were removed intact, with microscopically negative margins. The maximum tumor diameter was 8 and 9 cm, and the diagnosis of GIST was confirmed by positive CD117 and CD34 staining in both cases. Both tumors had a high (>5/50HPF) mitotic index. The patients had an uneventful postoperative course and were discharged on days 5 and 6. Both patients were started on imatinib 400 mg bid postoperatively. Postoperative magnetic resonance imaging and positron emission tomography computed tomography were carried out at 12 months and did not reveal any signs of recurrence. The patients are currently disease-free at 24 and 23 months of follow-up. In selected cases, complete excision of rectal GIST with negative margins is feasible via a trans-sphincteric approach. With the use of adjuvant therapy, which is currently advocated in all high-risk cases, it is possible that local excision with its reduced morbidity may become a viable alternative, especially in patients who would otherwise require abdominoperineal excision such as the two presented here. Prospective studies with longer follow-up are needed to confirm adequate oncologic results.