Tumors of the kidney may be classified according site as those arising in
the renal parenchyma and those originating in the renal pelvis. Tumors arising
in the parenchyma can be classified according to the cell of origin (histogenetic)
into those arising from epithelium (renal tubules and urothelium), messenchymal
tissue (renal interstitium) and embryonic tissue and according to biologic
behavior as benign or malignant.
Transitional epithelium lines the urinary tract starting from the renal pelvis
and extending through the ureter, the urinary bladder, and the proximal two-thirds
of the urethra. About 95% of tumors of the renal pelvis and the ureter are
epithelial in origin and 80% of these are malignant with transitional cell
carcinoma accounting for about 90%. Carcinomas occurring at both sites show
the same morphologic spectrum and clinical associations as those seen in the
urinary bladder. However, their combined frequencies are only about a tenth
of that of bladder carcinomas. The major prognostic features of cancers of
the pelvis and ureter are the same as those for bladder carcinoma and site
does not appear important. In view of these, tumors of the renal pelvis as
well as those of the ureter will be discussed with tumors of the bladder.
