– Uridinephosphorylase 1 (UPP1) is a member of the family of pentosyltransferase. UPP1 catalyses the reversible phosphorolysis of uridine to uracil. The expression levels and the enzymatic activity of UPP1 are higher in human solid tumors than in adjacent normal tissues. The high level of UPP1 expression in some tumors makes it a potential prognosticfactor for some cancers, such as oral squamous cell carcinoma. UPP1 is important for the homeostatic regulation of intracellular and plasma uridine concentratios. UPP1 plays an important role in the pyrimidine salvage pathway through its catalysis of the reversible phosphorolysis of uridine to uracil.