TYMP and cancer: Doxifluridine (5-deoxy-5-fluorouridine), a prodrug of 5-FU, which is converted to 5-FU via thymidine phosphorylase (TP), generates 5-FU preferentially in cancer,9 because various cancer tissues have higher levels of TP expression than adjacent non-neoplastic tissue.10,11 In addition, phase II trials showed that combination chemotherapy of gemcitabine and capecitabine (which is converted to 5-deoxy-5-fluorouridine in the liver and/or tumor tissue) had response rates ranging 30% to 48%,12–14 suggesting that they have synergistic effects.