Most spontaneous urinary bladder tumors in humans and chemical carcinogen-induced malignancies in experimental animals arise from epithelium over a long period of time. Our discussion of the cellular changes of neoplastic transformation will be based on a consideration of the biochemical ultrastructure of normal mammalian urinary bladder epithelium. To date, the majority of systematic studies on the ultrastructure of neoplastic transformation in urinary bladder have utilized laboratory and domestic animals. Some studies which have utilized human tissue have used controls which, retrospectively, were less than ideal and, in some instances, may have produced erroneous conclusions. For example, several early studies used, as normal controls, tissues from adolescents and young adults who died accidental deaths. Such studies led to the premature conclusion that the loss of asymmetric unit membrane plaques (AUM plaques), a mammalian bladder cell surface component, is a specific change associated with neoplastic transformation. This premise has 43been reexamined in light of the recent finding that there are significant ultrastructural alterations in human bladder epithelium that accompany physiological aging. It is now believed that AUM plaques, although a normal component of mammalian bladder epithelium in many species, decrease in number with physiological aging in humans and in other primates. Therefore, the specificity of AUM plaque deletion in carcinogenesis is open to question. It remains to be seen if other membrane components are similarily altered with physiological aging.
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