Found rare tumors that arise in the bladder fall naturally into two groups: rare histologies and tumor urothelial origin nonurothelial. Our discussion follows these lines, and took the unusual urothelial cancer in the first place, since these are by far the most common and clinically important. Most of what is called transitional cell carcinoma, about 80%, in fact, low histological grade and reflects mainly hyperplastic process. This process typically results in the papillary architecture of the mass thickness of cell proliferation, but not invasive. These injuries, known as "Ta", tend to recur and may progress to dysplasia and invasion in 15 to 20% of patients. However, for the most part, these tumors are more similar to polyps’ true carcinomas. An averlapping but definite pattern can be recognized in the remaining 20% of cases. In this group, high histological grade dysplasia and invasion are hallmarks.
These "non-papillary" cancers are the cause of most mortality, and show a significant range of histomorphology. In the end, they are so different from transitional cell carcinoma (TCC) that called for an alternative taxonomy. Although very rare as "pure" variant, the fact remains that about one third of non-papillary bladder cancers exhibit at least focal areas of unusual histologies discussed below. Therefore, in practice, there is considerable uncertainty about which of the cases showing lesser degrees of histological variant is considered really outside the normal spectrum of TCC, and should be classified as distinct entities.
These "non-papillary" cancers are the cause of most mortality, and show a significant range of histomorphology. In the end, they are so different from transitional cell carcinoma (TCC) that called for an alternative taxonomy. Although very rare as "pure" variant, the fact remains that about one third of non-papillary bladder cancers exhibit at least focal areas of unusual histologies discussed below. Therefore, in practice, there is considerable uncertainty about which of the cases showing lesser degrees of histological variant is considered really outside the normal spectrum of TCC, and should be classified as distinct entities.