Villous adenoma of the urinary bladder: a morphologic or biologic entity?

Villous adenomas in the urinary bladder are rare neoplasms whose malignant potential is unclear. A case of a morphologically benign non-invasive mucin producing papillary neoplasm of the urinary bladder associated with cystitis glandularis is presented. Absence of A tissue isoantigen from the neoplastic and metaplastic cells and the presence of H tissue isoantigen in both neoplastic and metaplastic cells is observed in a patient whose blood type is A, indicating incomplete maturation of surface coat constituents. The histologically benign appearance of this lesion may belie a malignant potential.