In an experimental study using C57BL mice and YM-12 fibrosarcoma, we found that a combination of UFT and radiation therapy was significantly more effective than both radiation therapy alone and 5-FU plus radiation therapy. In order to elucidate the mechanism behind this result, we attempted to measure concentrations of 5-FU in tumor tissue and serum of tumorbearing mice using the same experimental schedule as before. The results showed that the concentration of 5-FU was significantly higher in the tumor tissue of the mice treated with UFT than those treated with 5-FU, despite the fact that the concentration of 5-FU in the serum remained low in the two groups of mice. This result accounts for the higher response of the tumor in the mice to the combination of UFT and radiation than to that of 5-FU and radiation.
