Video Vignette: Demonstration of the effectiveness of neoadjuvant tyrosine kinase inhibitors in the treatment of rectal GIST, permitting downstaging and organ preservation

A 61-year-old female presented to her primary care provider with painless bleeding per rectum and pelvic fullness. Digital rectal exam noted an anterior 5-6 cm, firm, minimally-mobile mass in the distal rectum. Colonoscopy confirmed a 5 cm ulcerated mass 2-3 cm proximal and anterior to the dentate line. After failed endoscopic biopsy, a trans-anal biopsy demonstrated the lesion to be a spindle cell tumour with 1 mitosis/50 hpf and DOG+, CD KIT 117+, AML- , DESMIN - immunostaining consistent with a low grade gastrointestinal stromal tumor (GIST). MRI of the rectum confirmed a 5.6 cm anterior rectal lesion without evidence of regional or distant lymphadenopathy. The lesion was staged AJCC T3N0, low grade - Stage IB. Given its location, the patient underwent six months of neoadjuvant imatinib therapy, 400 mg/day to downstage the tumour (4 cm, yT2N0 - Stage IA) and enable organ-preservation (1). After six months, there was evidence of both a clinical and radiographic response and the patient was eligible for transanal resection via the TAMIS platform. A full thickness resection of the lesion was performed with clear margins and the defect was closed. The recovery was uneventful. Final pathology confirmed a low grade stromal tumour with moderate treatment affect and negative margins.