Gastrointestinal Stromal Tumor Of The Rectum Resected By Transanal Total Mesorectal Excision After Neoadjuvant Imatinib Treatment: A Case Report

This report describes the combination of a transanal total mesorectal excision (TaTME) and neoadjuvant therapy with Imatinib mesylate (IM) for a gastrointestinal stromal tumor (GIST) of the lower rectum. A 49-year-old man presented with a submucosal tumor with ulcer located 3 cm above the anal verge. Histopathologically, a biopsy showed spindle-shape cells, positive for C-kit and CD34, negative for smooth muscle actin, desmin and S-100 protein. Genetically, this GIST had the mutation in KIT exon 11. IM (400 mg/d) was administered as neoadjuvant therapy for 80 days. The GIST shrank from 4.7 to 3.3 cm in diameter. Abdominal and transanal approach were started at the same time. The tumor was resected by TaTME successfully. The manometric pressure data and anal function were preserved before and after surgery. TaTME and neoadjuvant therapy with IM provide a treatment option which can preserve anal function for the lower rectal GIST.