Elevations of thymidylate synthetase activity in stomach cancer tissue with preoperative continuous intravenous infusion of 5-fluorouracil

5-fluorouracil (5-FU) is one of the key drugs of chemotherapy for many kinds of human cancer. One of the mechanisms of action of 5-FU has been explained in terms of inhibition of thymidylate synthetase (TS). However, correlation between the antitumor activity of 5-FU and changes in TS is not yet clear. In this study 5-FU was continuously administered intravenously to seven patients with advanced stomach cancer in a daily dose of 500mg for preoperative seven days (CIV group). Six patients without preoperative chemotherapy were also examined (control group). In cancerous lesion TS-binding and TS inhibition rate (TSIR) of CIV group were higher than control group. In non-cancerous areas TS-binding and total-TS of CIV group were higher than control group. The mechanism of preoperative chemotherapy should be explainedusing additional parameters.