Inverted urothelial papilloma: a lesion with malignant potential.

Two cases of inverted urothelial papilloma are presented. In the first case the inverted papilloma was in the ureter and varying degrees of cellular atypia were demonstrated on histology: 7 years later, a single bladder lesion consisting of papillary transitional cell carcinoma and inverted papilloma developed in the same patient. In the second case a bladder tumor consisting of inverted papilloma mixed with papillary infiltrating transitional cell carcinoma was detected. The peculiar morphological findings, histogenesis and biological behavior of inverted urothelial lesions are discussed.