Uridine phosphorylase in breast cancer: a new prognostic factor?

Uridine phosphorylase (UPase) is an enzyme that converts the pyrimidine nucleoside uridine into uracil. Upon availability of ribose-1-phosphate, UPase can also catalyze the formation of nucleosides from uracil as well as from 5-fluorouracil, therefore involved in fluoropyrimidine metabolism. UPase gene expression is strictly controlled at the promoter level by oncogenes, tumor suppressor genes, and cytokines. UPase activity is usually elevated in various tumor tissues, including breast cancer, compared to matched normal tissues and this induction appears to contribute to the therapeutic efficacy of fluoropyrimidines in cancer patients. In this review, we will discuss in detail the role of UPase in the activation of fluoropyrimidines and its effect on the prognosis of breast cancer patients.