Review of papillary renal cell carcinoma with focus on clinical and pathobiological aspects.

Recent studies have shown that papillary renal cell carcinoma (RCC) is clinically and genotypically a distinct entity. Papillary RCCs account for about 10-15% of renal parenchymal neoplasms. Macroscopically, the cut surface is yellow or brown in color and large tumors frequently show cystic change. Hemorrhage and necrosis are common. Histologically, Delahunt and Eble have classified papillary RCCs into type 1 (small cells, single layer) and type 2 (large cells, pseudostratification) according to the cytoplasmic volume and thickness of the lining cells. In chromosomal analysis, gain of chromosomes 7 and 17, loss of Y chromosome and additional gains (chromosome 3q, 8p, 12q, 16q and 20q) are frequently found in type 1 papillary RCCs, but the chromosomal aberration of type 2 papillary RCCs seems to be more heterogenous than that of type 1 papillary RCCs. Mutations of MET proto-oncogenes in some cases of both hereditary and sporadic papillary RCCs have recently been detected. Furthermore, all hereditary and sporadic papillary RCCs with MET proto-oncogene show type 1 histological features. Type 1 papillary RCCs generally seem to have a favorable prognosis, but type 2 tumors have a worse prognosis than do type 1 tumors. Papillary RCCs with involvement of the X chromosome and cancer syndrome with predisposition to cutaneous/uterine leiomyomas and papillary RCCs, the histological features of which are basically different from those of usual papillary RCCs, have also been recently reported. Since papillary RCCs seem to constitute clinically, histologically, and even genetically more heterogenous groups than previously thought, further investigations are needed to characterize the subtype of papillary RCC.