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BACKGROUND Thymidine phosphorylase (TP), which is identical to platelet‐derived endothelial cell growth factor (PD‐ECGF), stimulates chemotaxis of endothelial cells and is involved in the angiogenesis of human solid tumors. METHODS The activity and expression of TP were examined in human transitional cell carcinomas (TCCs) of the bladder, and their association with clinicopathologic findings was determined. The activity of the enzyme in 37 TCCs and 12 adjacent nonneoplastic tissues was measured spectrophotometrically. The expression of TP was also examined by immunoblotting. Immunohistochemical analysis was performed on 108 TCCs. RESULTS TP activity in the carcinomas was higher than that in adjacent normal tissues (P = 0.002). TP activity in Grade 3 tumors or those classified as pT2–4 was higher than in Grade 1 and 2 tumors (P = 0.017) or those classified as pT1 (P = 0.007). The level of expression of TP detected by immunoblotting correlated well with TP activity. Immunohistochemical analyses showed that 62 of 108 cases (57.4%) were TP positive. There was a significant correlation between TP expression and histologic grade, infiltration pattern, local invasion, and lymph node metastasis. TP expression as a prognostic variable was studied using the Cox proportional hazards model. TP overexpression was an independent prognostic factor, as were lymph node metastasis and local invasion. CONCLUSIONS These findings suggest that TP activity and its level of expression influence the progression of TCC and the prognoses of patients with this disease. Cancer 2000;88:1131–8. © 2000 American Cancer Society.

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