A complete response to a new chemotherapeutic agent, S1, was achieved in a 64-year-old Japanese man with advanced transverse colon cancer. S1 is a combination of the agents tegafur, 5-chloro-2,4-dihydroxypyridine, and oxonic acid. Because the patient was considered to be a high operative risk due to his poor general condition, S1 was administered at 100 mg/day for 5 days/week over 12 weeks. However, as the serum carcinoembryonic antigen level continued to gradually increase, partial resection of the transverse colon was finally performed. Histopathological study of the resected specimen showed mucin pools in the colon wall with no residual viable cancer cells. No perioperative complications were recognized and the patient is now leading a normal life 6 months after his operation without any signs of recurrence.
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