Diffuse papillomatosis of rat urinary bladder occurring in association with vesical calculi.

Repeated intravesical administrations of 0.9 per cent NaCl solution with or without bladder carcinogen N-butyl-N-(3-carboxypropyl)nitrosamine resulted in a high incidence of calculus formation in the urinary bladder. In all such cases, diffuse papillomatosis of the bladder urothelium was observed. "Invasion" of the tunica muscularis and the tunica adventitia by tumor was demonstrated as early as week 9 of the experiment. Morphologically, the lesions could not be distinguished from the bladder tumors induced by an orally administered carcinogen. Evidence was presented to conclude that they represent neoplasms of low malignant potential. The results indicate that bladder tumors may develop in the absence of known exposure to carcinogen provided the urothelium is chronically stimulated. Tumors solely attributable to N-butyl-N-(3-carboxypropyl)nitrosamine treatment did not occur.