TYMS and hepatocellular carcinoma: On the basis of increased expression of thymidylate synthase (TYMS), thymidine kinase 1 (TK-1), and equilibrative nucleoside transporter 1 (SLC29A1) in HCC compared with liver tissue, we conducted a proof-of-concept study evaluating the efficacy of 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) PET to assess response to TACE.