[A Case of Locally Advanced Rectal Cancer Successfully Treated by Conversion Surgery after Multidisciplinary Treatment].

A 70-year-old woman who complained of abdominal pain and a prolapsed tumor from the anus was diagnosed with an intestinal obstruction resulting from anal canal cancer. Computed tomography (CT) and magnetic resonance imaging revealed a huge tumor (11×5×12 cm) invading the vagina and levator ani muscle. Enlarged inguinal lymph nodes on both sides indicated metastasis. The clinical stage was T4b (vagina, levator ani muscle, and pudenda) N0H0M1a (LYM), stage IV (Japanese Classification of Colorectal Carcinoma: 8th edition). As curative resection was not possible, a transvers colostomy was performed to relieve the intestinal obstruction. This was followed by chemoradiotherapy (45 Gy/1.8 Gy×25; TS-1, 80 mg/body for 2 weeks and a 1-week interval, for 2 courses) and up to 10 courses of Bev+mFOLFOX6 continuously. After this regimen, there was a remarkable reduction in tumor size. Positron emission tomography-CT revealed no FDG uptake in the primary rectal site or inguinal lymph nodes, but a maximum standardized uptake value (SUVmax) of 6.3 was detected in the vagina. Six weeks after chemotherapy, the patient underwent a pelvic exenteration including resection of the vagina, bladder, and pudenda. The pathological stage was yp T4b (vagina) N0H0M0, stageⅡ. Curative resection was performed, and the patient had a Grade 2 pathological response after chemoradiotherapy.