Uroplakins (UPs) are a family of transmembrane proteins (UPs Ia, Ib, II and III) that are specific differentiation products of urothelial cells. In non-neoplastic mammalian urothelium, UPs are expressed in the luminal surface plasmalemma of superficial (umbrella) cells, forming complexes of 16nm crystalline particles. UPIII is specific for tumors of urothelial origin and, when used in combination with other markers, can aid in the diagnosis of primary and metastatic tumors

Uroplakin III is a 47 kDa glycoprotein present in the urothelial surface membrane of human renal pelvis, ureter, bladder and urethra.

Studies have shown that UPIII is highly specific for identification of primary and metastatic urothelial carcinomas. However, the sensitivity of UPIII in detection of urothelial carcinoma is moderate. Combined use of a panel of antibodies is important in the diagnosis of urothelial tumors.