Squamous and transitional elements in rat bladder carcinomas induced by N-butyl-N-4-hydroxybutyl-nitrosamine (BBN). A...

Three hundred rat bladders bearing tumors induced by N-butyl-N-4-(OH)butyl-nitrosamine (BBN) were examined by routine histologic study and immunohistochemical staining of intermediate filament types. Smaller lesions were similar to human urothelial dysplasia histologically and immunohistochemically. Progression of the lesions demonstrated large exophytic papillomas with extensive endophytic epithelial growth into abundant stroma. These lesions showed increasing predominance of squamous over transitional elements. Immunohistochemical findings confirmed these results and also demonstrated that morphologically indifferent cells, even in early lesions, express heavier cytokeratins characteristic of keratinizing squamous epithelium. These results demonstrate that BBN-induced bladder tumors show marked quantitative and qualitative differences from the most common, purely transitional, human bladder carcinomas. However, the development in BBN-treated rat bladders of two tumor types, squamous and transitional, from an altered urothelium may serve as an attractive model for further study of the molecular genetics of keratin expression.