Abstract
Cancer of unknown primary (CUP), a rare and aggressive clinical entity, accounts for approximately 3% of all malignancies. CUP with urothelial origin is even more unusual, with no other cases reported in the current literature. As imaging and other studies often do not reveal the tumor origin, the approach to CUP involves a focused search for the primary tumor, relying on guidance from immunohistochemical staining of biopsy specimens. Treatment consists of standard therapies directed at the most likely tumor origin.