[S-1 as a single agent for colorectal cancer].

Chemotherapy for colorectal cancer is now improving rapidly due to new drugs like oxaliplatin and molecular targeting drugs. The key drug, however, is still 5-fluorouracil (5-FU). S-1 is an oral 5-FU anti-tumor drug that combines three pharmacological agents: tegafur, 5-chloro-2,4-dihydroxypyridine, which inhibits dihydropyrimidine dehydrogenase activity, and potassium oxonate, which reduces gastrointestinal toxicity. The results of the phase II study suggested that S-1 as a single agent was active against metastatic colorectal cancer: CR rate was 36-40% and MST was about one-year. Toxicity was all tolerable. Clinical trials of S-1 with oxaliplatin or CPT-11 combination chemotherapy are ongoing in Japan. S-1 with molecular targeting drugs will also be studied. Therefore, S-1 is expected to play an important part in chemotherapy for colorectal cancer.