Pathology of human bladder cancer and related lesions

The lower urinary tract consists of the renal pelves, ureters, urinary bladder, and urethra. It is lined by a distinctive epithelium as described below and functions as a passageway and a storage area for the excretion of urine. Tumors of the lower urinary tract are fairly common, particularly in males, making up over 4% of all new cancers in the U.S. each year. The classification of these tumors should have been a rather simple matter, since they are readily accessible for clinical and morphological examination, their structural variation is limited, and there is an extensive literature describing their morphology, biology, and treatment. Despite the suggestions of many authors, however, there is today no generally accepted system for the classification of these tumors. A bewildering variety of terms have been used in the literature, and comparisons of the biology and of the treatment results between one series of cases and another is difficult. In this review, we will briefly describe some of the classification systems that have been proposed, then focus on one which has been used for the past few years 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. Certain less-common benign and neoplastic lesions occurring in the lower urinary tract will be discussed as well as some of the technical aspects of processing and examining these samples.