TYMS and neoplasm: In a rodent model, S-1 doses that were equitoxic to UFT doses resulted in higher 5-FU levels, as revealed by the following pharmacokinetic measurements: single-day area under the curve (AUC0–24) of 5-FU in plasma (3.5-fold), AUC0–24 of 5-FU incorporated into tumour RNA (1.3-fold), and tumour thymidylate synthase inhibition rate (∼20%).