Anorectal Gastrointestinal Stromal Tumor: A Case Report and Literature Review

Abstract

Gastrointestinal stromal tumors or “GIST” are mesenchymal neoplasms expressing KIT(CD117) tyrosine kinase and showing the presence of activating mutations in KIT or PDGFRα (platelet-derived growth factor alpha). GIST of anal canal is an extremely rare tumor, accounting for only 3% of all anorectal mesenchymal tumors and 0.1–0.4% of all GIST. GIST with large tumor size and high mitotic activity are highly malignant, but the biological behavior of anorectal GIST is less clear. Abdominoperineal resection (APR) or conservative surgery is the best treatment option. Imatinib mesylate, a tyrosine kinase inhibitor, has shown promising results in its management. We present a case of anorectal GIST diagnosed by computed tomography (CT) scan, magnetic resonance imaging (MRI), and colonoscopy with biopsy. The patient underwent abdominoperineal resection (APR) and was confirmed on histopathology to have anal canal GIST with tumor size more than 5 cm in maximum dimension and mitotic figures more than 5/50 high power field (HPF). The CD117—immunoreactive score—was 3+ in spindled cells. Therefore the patient was put on adjuvant imatinib mesylate 400 mg daily.

Wide local excision for anal GIST: A case report and review of literature

“…While large, aggressive tumors require APR [8], [9]. But, sometimes as the patients are often elderly and not willing for a permanent colostomy, the question of whether local excision can be considered in these patients remains to be answered.…”

“…It has been shown to downstage the disease when used as neoadjuvant therapy and facilitate organ and function preserving surgeries especially in cases of rectal GIST [14]. However, it has been used only as an adjuvant therapy after curative resection for anal GIST in previous studies [8], [10]. Future studies with use of imatinib as preoperative treatment for anal GIST are required to determine its potential in avoiding radical surgery.…”

“…Anal region is the primary site of origin in only 2% of all anorectal GIST cases [3]. Due to its potential for malignant behavior, most of the previously reported cases were treated by radical surgery such as abdominoperineal resection (APR) and pelvic exentration [4], [5], [6], [7], [8], [9], [10]. But some anecdotal cases have been treated successfully by local excision [1], [11], [12].…”

Tumors and Tumorlike Conditions of the Anal Canal and Perianal Region: MR Imaging Findings

“…Gastrointestinal stromal tumors of the anal canal are rare, accounting for 0.1%-0.4% of all gastrointestinal stromal tumors (55). Gastrointestinal stromal tumors arise from the interstitial cells of Cajal of the myenteric plexus, which control gastrointestinal tract motility.…”

Gastrointestinal Stromal Tumors in the 21<sup>st</sup> Century

“…Regarding rectal GISTs, there is debate whether conservative therapy is equal to abdominoperineal resection, as survival and the rate of distant metastasis is reported to be similar [76]. Other authors suggest that all rectovaginal GISTs require a biopsy with excision regardless of the size due to the risk of increased mortality [45].…”