[A case of advanced colon cancer with peritoneal dissemination completely responding to TS-1].

A 55-year-old man was referred to us after transverse colostomy for intestinal obstruction caused by descending colon cancer with peritoneal dissemination. The colon lesion was palpated as a well-defined hard mass in the left lower abdomen and the disseminated lesion as a hard mass with an unclear border in the right lower abdomen. CEA level was 917 ng/ml at admission. Left hemicolectomy was performed for tumor reduction and TS-1 of 120 mg/day was started 6 days after surgery (4 weeks administration followed by a 2-week rest period). Administration discontinued due to nausea 4 weeks after commencement of the therapy, and restarted as a 2-week administration followed by a 2-week rest period. There has been no adverse reaction since then. Twenty-seven weeks after surgery, CEA level was reduced to 47 ng/ml and peritoneal dissemination was found to have disappeared upon physical examination and computed tomograph. TS-1 is expected to be an effective agent for the treatment of colon cancer with peritoneal dissemination.