Papillary tumors of the bladder.

The most common neoplasms of the urinary bladder are papillary tumors that vary histologically and cytologically from very well differentiated to highly anaplastic patterns. Biologic behavior of these tumors is closely correlated with morphology, so that cytologically benign tumors (papillomas) are benign in behavior, and increasing anaplasia is associated with increasing clinical aggressiveness. By this definition, 20% or more of bladder tumors should be classified as papillomas. The development of carcinoma occurs in a series of steps, progressing through atypia and carcinoma in situ to invasion. Finally, evidence is presented to show that invasive carcinoma often begins from areas of flat carcinoma in situ associated with, but not within, co-existing papillary tumors.