ABSTRACT
This chapter describes some of the classification systems of urinary tract tumors, and focuses on one which has been used in the Central Pathology Laboratory of the National Bladder Cancer Collaborative Group A, an aggregate of investigators representing some ten institutions entering patients into a cooperative study. It discusses certain less-common benign and neoplastic lesions occurring in the lower urinary tract as well as some of the technical aspects of processing and examining these samples. The wall of the lower urinary tract, from renal pelvis to urethra, consists of four distinct layers, epithelium, basement membrane, subepithelial connective tissue, and muscle. Tumors of the lower urinary tract are first subdivided according to their origin, either from epithelium or from mesenchymal elements. Undifferentiated carcinoma of the lower urinary tract is essentially a diagnosis of exclusion. The presence of endothelial cell nuclei on the inner surface of the vessel-like structure is helpful in making the diagnosis.
