Thymidylate synthase in advanced gastrointestinal and breast cancers.

Knowledge of population thymidylate synthase (TS) levels in malignant tumors and normal tissues is essential for the use of TS as a predictor for 5-fluorouracil treatment. Tumor tissue TS levels in fresh frozen surgical biopsies from 136 patients with gastrointestinal or breast cancer, not previously subjected to chemotherapy, were analysed by [3H]FdUMP radioligand binding assay. TS levels were 2.4 +/- 0.31 pmol/g in liver metastases of colorectal cancer (n = 87), 4.2 +/- 1.0 pmol/g in primary colorectal cancer (n = 13), 2.7 +/- 0.93 pmol/g in gastric cancer (n = 13), 3.1 +/- 1.7 pmol/g in pancreatic cancer (n = 10), 3.4 +/- 1.4 pmol/g in breast cancer (n = 13) and 0.58 +/- 0.075 pmol/g in normal liver parenchyma (n = 24). TS levels were significantly higher in malignant tumor tissues compared to normal liver parenchyma.