Clinical evaluation of S-1, a new anticancer agent, in patients with advanced gastrointestinal cancer. S-1 Cooperative Gastrointestinal Study Group

In developing a new anticancer agent, it is most important to balance the antitumor activity and toxicity of the agent. S-1 was designed to achieve high activity and low toxicity. In it tegafur, a prodrug of 5-FU, is combined with two classes of modulators. CDHP, an inhibitor of 5-FU degradation in the liver, and Oxo, an inhibitor of 5-FU phosphoribosylation in the digestive tract. In both early and late Phase II studies, S-1 was effective against advanced or recurrent gastrointestinal cancer. Toxicities were generally mild, and there were no toxic deaths.