Ultrastructure of tumors induced in the rat urinary bladder by nitrosomethyldodecylamine.

N-Nitroso-N-methyl-n-dodecylamine (NMDA) is a powerful carcinogen in the rat and the Syrian golden hamster. In both species the urinary bladder is the main target organ. We studied the ultrastructure of these bladder tumors in the Fischer rat in some detail, since this compound provides an interesting model for carcinogenesis in the urinary bladder. We found that the proliferating basal layers of the transitional cell carcinomas were undergoing squamous metaplasia, which indicates that squamous carcinomas in the organ may arise from pre-existing transitional cell tumors.