Which is the best surgical approach for anorectal gastrointestinal stromal tumors in the post-imatinib era?

Abstract

Anorectal gastrointestinal stromal tumors (GISTs) represent about 5 % of all GISTs. Local recurrence, although with a long latency period, occurs in more than a half of cases and is a major concern. Prognostic factors for recurrence are the tumor size and the mitotic index. However, for anorectal lesions, the particular location represents a main obstacle to achieving a radical (R0) resection. Surgery is the treatment of choice for patients with localized or potentially resectable GIST lesions. The goal is to achieve complete gross resection of the tumor with an intact pseudocapsule. Current guidelines recommend wide resection with clear margins (such as abdominoperineal or anterior resection) [1, 2]. Local removal of the tumor has also been proposed, performed by a transanal, transsacral, or transvaginal approach, even if abdominal surgery is more likely to result in negative margins than local surgery [3]. In the article by Centonze et al. [4], a new local technique has been proposed for anorectal GIST excision. A transsphincteric approach was used, with a right ischiorectal fossa incision. Although in the two cases presented the tumor size was C8 cm and the mitotic index was high, the procedure seems feasible, with low morbidity and good early oncological outcomes. Both the patients underwent adjuvant therapy with imatinib, as recommended for high risk GISTs. There are two important considerations to be made. The first concerns the preoperative workup. All anorectal GIST patients should be managed by a multidisciplinary team with expertise in sarcoma. The workup should include: history, physical examination, abdominal/pelvic computed tomography (CT) scan with contrast and/or magnetic resonance imaging (MRI), and chest imaging. A positron emission tomography (PET) scan is not a substitute for CT, however, it may be used to clarify ambiguous findings seen on CT or MRI. Finally, endoscopic ultrasound-guided fine needle aspiration biopsy is necessary to confirm the diagnosis of primary GIST prior to the initiation of any preoperative therapy [5]. The second concerns the use of imatinib associated with surgery. This selective inhibitor of the KIT protein tyrosine kinase has drastically improved the prognosis of patients with GIST. The results of a recently completed trial suggest that in patients with a high risk of recurrence adjuvant imatinib administered for 36 months significantly improves relapse-free and overall survival compared to 12 months of imatinib therapy [6]. Since sphincter-sparing surgery is a primary goal in treating rectal tumors, the use of preoperative imatinib has also been investigated. The published trials show that preoperative imatinib is safe, and associated with a higher R0 rate, lower risk of tumor rupture, acceptable perioperative morbidity, and good disease-free survival [7–10]. However, the survival benefit is not well determinable since most of the patients included in these studies also received imatinib postoperatively for at least 2 years [7–9]. Thus, at the present time, the decision to use preoperative therapy for patients with resectable primary, locally advanced, or recurrent GIST should be made on an individual basis. In our opinion, patients with high risk anorectal GIST (tumor size > 5 cm and/or documented mitotic rate > 5 mitoses/50 high power field) should be treated with preoperative imatinib, followed by sphincter-saving surgery. Adjuvant imatinib for high-risk patients should be S. Pucciarelli (&) I. Maretto Clinica Chirurgica I, Department of Surgery, Oncology, and Gastroenterology, University of Padua, Via Giustiniani, 2, 35128 Padua, Italy e-mail: puc@unipd.it