TYMP and nonpapillary renal cell carcinoma: With the knowledge that ccRCC tumors are considered unresponsive to anticancer cytotoxic drugs that are active in other malignancies, along with the need to identify cytotoxic drugs that can potentially further enhance the antitumor activity of biologically targeted molecules, the overexpressed thymidine phosphorylase in ccRCC is being introduced as a target for the activation of 5-Fluorouracil pro-drug.