Thymidine phosphorylase (TP) is identical to platelet-derived endothelial cell growth factor (PD-ECGF). TP has an angiogenic activity and confers resistance to hypoxia-induced apoptosis on cells. TP expression is correlated with microvessel count, invasion and poor prognosis in many solid tumors. TPI, an inhibitor of TP, suppresses growth and metastasis of tumors by inhibiting the effect of TP.