[Pathological Complete Response Following Chemotherapy for Sigmoid Colon Cancer with Para-Aortic Lymph Node Metastasis-A Case Report].

A man in his 50s visitedour hospital with complaints of frequent urination, painful micturition, macrohematuria, and weight loss. On examination, he was diagnosed with RAS-wild-type sigmoid colon cancer invading the urinary bladder, ureter, andexternal iliac artery, with para-aortic lymph node metastasis(T4b, NX, M1a, Stage ⅣA according to the Union for International Cancer Control 8th edition guidelines)andsigmoid -vesical fistula. Thus, sigmoidcolostomy was performed. Postoperatively, S-1 plus oxaliplatin was administered. After 3 courses of chemotherapy, the primary tumor and para-aortic lymph node metastases shrunk. Moreover, after 8 courses of chemotherapy, further shrinkage of the primary tumor and paraaortic lymph node metastases was confirmed; however, tumor markers in the blood increased. Therefore, the patient received 3 additional courses of S-1 plus oxaliplatin plus cetuximab, which resultedin complete response. Sigmoidectomy, partial cystectomy, ureterectomy, resection of the external iliac artery, andreconstruction using a prosthetic vascular graft were performed. Subsequent pathological examination revealed no viable cancer cells(pathological response), achieving R0 resection. The patient has been followedup for 2.5 years after the curative resection, with no recurrence.