Thymidylate synthase expression in circulating tumor cells: a new tool to predict 5-fluorouracil resistance in metastatic colorectal cancer patients.

Thymidylate synthase (TYMS) is an important enzyme for 5-fluorouracil (5-FU) metabolism in metastatic colorectal cancer (mCRC) patients. The search for this enzyme in circulating tumor cells (CTCs) can be a powerful tool to follow-up cancer patients. mCRC patients were enrolled before the beginning of 5-FU-based chemotherapy.