Thymidylate synthase inhibition as a predictor of tumor sensitivity of fluorinated pyrimidines.

The thymidylate synthase (TS) content of tumor tissue was assayed and the levels of 5-fluorouracil (5-Fu) in serum and tumor tissue were determined in 21 patients with cervical cancer who were treated with UFT, a fluorinated pyrimidine. Subrenal capsule assay, a predictive tumor sensitivity test, was conducted concurrently on cervical tumor samples. TS inhibition and serum and tissue 5-Fu levels widely varied between both samples. Investigation of the relationship between the tumor growth inhibition rate determined by subrenal capsule assay and the above parameters (TS inhibition, serum and tissue 5-Fu levels) showed that TS inhibition and tumor growth inhibition were well correlated (r = 0.73). This suggests that a TS inhibition assay in tumor tissue can be a useful predictive test for tumor sensitivity of fluorinated pyrimidines.