The pathology of renal epithelial neoplasms.

Renal epithelial neoplasms are morphologically diverse and are characterized by distinct genetic abnormalities. In addition, our understanding of these morphologic differences has allowed us to develop a classification scheme that is more in keeping with their clinical behavior. Clear cell carcinoma is the most common type of renal cell carcinoma (RCC) and accounts for the majority of cases that develop metastatic disease. Papillary carcinoma does not constitute a single morphologic, clinical, or genetic entity with some variants being highly aggressive while others are quite indolent. Chromophobe RCC constitutes less than 10% of primary cases and appears to have a more indolent behavior than clear cell or papillary carcinoma. Oncocytomas are benign, but some cases may be difficult to distinguish from eosinophilic variants of chromophobe RCC. RCC, type unclassified, constitutes up to 7% of cases and represents a histologically and clinically heterogeneous category of tumors that does not fit neatly into any of the other well-defined categories. We have entered the era in which pathologists apply their expertise in microscopy and in evaluating antigenic expression in complex cellular systems to aid in the development and characterization of targeted therapy.