Biological role of thymidine phosphorylase in human astrocytic tumors

Thymidine phosphorylase (TP) has strong angiogenic activity and is overexpr essed in a wide variety of malignant tumors. To elucidate the role of TP in human astrocytic tumors, we immunohistochemically investigated the express ion of TP in 62 astrocytic tumors (12 astrocytomas, 12 anaplastic astrocyto mas and 38 glioblastomas). Fifty-five astrocytic tumors (88.7%) were immuno positive for TP. The level of TP-expression was significantly correlated wi th the malignancy grade of astrocytic tumors; most of malignant gliomas hig hly expressed TP, while a small number of cells were positive in low grade astrocytomas (p < 0.001). Using double-immunostaining, we clarified that TP -expression was predominantly detectable in macrophages. There was no signi ficant correlation between MIB-1 labeling index and TP-expression. However, TP-expression and the microvessel density were well correlated. These sugg est that TP, mainly produced by the infiltrated macrophages, may play an im portant role in the progression of astrocytic tumors via neovascularization . Inhibitor of TP may represent a therapeutic modality for treating maligna nt gliomas.