A case of pathological complete response of advanced rectal cancer to preoperative chemoradiotherapy using S-1

In patients with advanced rectal cancer, preoperative chemoradiotherapy is superior to postoperative chemoradiotherapy because of causing less toxicity and achieving higher rates of sphincter preservation and curative resection. We treated a patient who had advanced rectal cancer with preoperative chemotherapy using S-1 and concurrent radiotherapy. S-1 was orally administered at a dose of 100 mg/day during the first cycle (two-week on and one week off). During the third cycle, radiotherapy was initiated concurrently and a total dose of 45 Gy was given. The most severe adverse event was grade 3 leukopenia during the third cycle. On day 42 after completing radiotherapy, low anterior resection with diverting colostomy was performed. Histological examination found no viable cancer cells in the resected specimens, including the primary tumor site and lymph nodes. Thus, a pathological complete response was achieved. Postoperatively, anastomotic leakage occurred, but it was resolved with transanal drainage. Preoperative chemoradiotherapy using S-1 contributed to sphincter preservation and curative resection in this patient. This regimen was both effective and well-tolerated, suggesting that it could be useful for advanced rectal cancer.