Modifying factors in urinary bladder carcinogenesis.

N-Butyl-N-(4-hydroxybutyl)nitrosamine (BBN) is a potent carcinogen in the urinary bladder of animals. The BBN model of bladder cancer is an excellent model of human urinary bladder cancer and has already led to a greater knowledge of its pathogenesis. In our studies, histogenesis and morphological characteristics of BBN urinary bladder cancer were analyzed in different animal species such as rats, mice, hamsters and guinea pigs and also in different rat strains. Papillary or nodular hyperplasia (PN hyperplasia) is found to be a preneoplastic lesion of the rat urinary bladder. Therefore, the promoting and inhibitory effects of various chemicals in two-stage urinary bladder carcinogenesis were judged by measuring PN hyperplasia in rats. Dose-dependent and organ-specific effects of the urinary bladder promoter, saccharin, in the induction of PN hyperplasia were shown in rats after initiation by BBN. The promoting effect of saccharin was seen more clearly in the urinary bladder of rats after potent initiation. A strain difference in susceptibility of the urinary bladder to the promoter was also shown. These results suggest that the above various factors may also have modifying activities on urinary bladder carcinogenesis in man.