The pathogenesis of bladder cancer.

Carcinoma of the urinary bladder appears to arise, in at least some cases, from carcinoma in situ developing in a field of atypical epithelial proliferation. There is both a spatial and temporal relationship between invasive and in situ bladder cancer, although the exact relationship between the noninvasive flat and papillary types of tumors is not known. Prenoeplastic bladder lesions are defined as irreversible, although not necessarily progressive, and an experimental animal model of the disease has been developed. The appearance of pleomorphic microvilli on the luminal surface of epithelial cells of the urinary bladders of Fischer rats is correlated with the irreversibility of hyperplastic epithelial lesions induced by feeding N-[4-(5-nitro-2-furyl)-2-thiazolyl] formamide (FANFT) to the test animals. This alteration can be visualized by scanning electron microscopy of cytologic and histologic preparations.