Gastrointestinal stromal tumor of the rectum treated with neoadjuvant Imatinib followed by transanal endoscopic microsurgery

INTRODUCTION

The gastrointestinal stromal tumor (GIST) is a rare type of tumor that expresses CD117 oncogene that can be detected by immunohistochemistry². The most common sites of GISTs are stomach (70%), and small intestine (20%), while rectum is comprised in only 3% of the cases⁵. Although a rare condition, the GIST located in the distal rectum may require an abdominoperineal resection. There is no data to support the use of Imatinib (Gleevec from Novartis, Basel, Switzerland), a selective inhibitor of tyrosine quinase, as neoadjuvant therapy. However, the last session consensus for the treatment of GIST, suggests that this form of therapy can be used in some cases where anal sphincter is involved⁷. The objective of this report is to describe a case of GIST distal rectum in the rectovaginal septum with partial invasion of the anal sphincter, which was successfully treated by neoadjuvant therapy with imatinib followed by the technique of transanal endoscopic microsurgery (TEM). The results are compared with experience in the literature.

CASE REPORT

A 63-years-old female patient was sent to the hospital with complaints of mild constipation. A clinical examination did not detect any palpable abdominal mass. Rectal digital exam revealed a 5 cm mass in the left anterior rectal wall, located 2 cm above the dentate line. The mass was solid, with a smooth and regular surface. Colonoscopy confirmed the presence of a round and regular mass, covered by normal mucosa, measuring about 5 cm in diameter, in the left anterior wall. A transrectal biopsy with Tru-cut needle was performed. Immunohistochemical positivity for CD117 and CD34 antigens, and negative for smooth muscle actin or S-100 protein confirmed the diagnosis of a submucosal rectal GIST. The mitotic activity was 2×10 high power field (HPF), and there was absence of necrosis. Computed tomography showed the presence of a tumor of 5.2x5.0x5.6 cm, irregular, with eccentric thickening of the left anterior rectal wall in the lower rectum, with close contact with the posterior vaginal wall and partial invasion of the levator ani muscle, but with no evidence of lymph node or distant metastases (Figure 1).