Diagnosis and Treatment of Rectal Gastrointestinal Stromal Tumors.

A 69-year-old man presented with a rectal mass that was noted on physical examination. Flexible sigmoidoscopy confirmed the presence of a well-defined mass 3 cm from the anal verge (). Magnetic resonance imaging of the pelvis identified a 5.8-cm heterogeneous mass with intersphincteric extension. Positron emission tomography-computed tomography revealed no evidence of distant metastatic disease. Endoscopic ultrasound (EUS) with fine-needle aspiration revealed a noncircumferential submucosal hypoechoic mass () with pathology significant for spindle cells staining positive for CD117, consistent with a GI stromal tumor (GIST). The patient received 5 months of neoadjuvant imatinib with great response () and subsequently underwent transanal endoscopic microsurgical resection. He continues on adjuvant imatinib and is currently without signs of recurrence at 18 months postprocedure; he is undergoing restaging CT chest/abdomen/pelvis and surveillance flexible sigmoidoscopy every 6 months.