Platelet-derived endothelial cell growth-factor (PD-ECGF) is similar to the pyrimidine enzyme thymidine phosphorylase (TP). A high TP expression at tumor sites is correlated with tumor growth, induction of angiogenesis, and metastasis. Therefore, high TP is most likely associated with a poor prognosis. TP is not only expressed in tumor cells but also in tumor surrounding tissues, such as tumor infiltrating macrophages. TP catalyzes the conversion of thymidine to thymine and doxyribose-1-phosphate (dR-1-P). The latter in its parent form or in its sugar form, deoxyribose (dR) may play a role in the induction of angiogenesis. It may modulate cellular energy metabolism or be a substrate in a chemical reaction generating reactive oxygen species. L-deoxyribose (L-dR) and thymidine phosphorylase inhibitor (TPI) can reverse these effects. The mechanism of TP induction is not yet completely clear, but TNF, IL10 and other cytokines have been clearly shown to induce its expression. The various complex interactions of TP give it an essential role in cellular functioning and, hence, it is an ideal target in cancer therapy.