[Non clear cell renal cell carcinoma. 2008 update in renal tumor pathology]

Non clear cell renal cell carcinomas represent almost 20% of all renal neoplasms. Their classification is continuously being adjusted according to new cytogenetic and molecular data. Since molecular techniques are expensive, diagnosis still relies on morphological and immuno-histochemical criteria detailed hereby. Papillary renal cell carcinomas are the most important group and its classification is more and more complex. It encompasses low-grade papillary carcinomas (type 1 papillary renal cell carcinoma, oncocytic papillary renal cell carcinoma) and high-grade papillary carcinomas (type 2 papillary renal cell carcinoma, juvenile papillary carcinoma corresponding to renal carcinoma associated with Xp11.2 translocations and unclassified carcinomas). Mucinous tubular and spindle cell carcinoma and tubulocystic carcinoma are new entities, actually considered by some authors as low-grade papillary carcinomas. The so-called carcinoma of collecting ducts of Bellini and renal medullary carcinoma should be considered as intrarenal urothelial carcinoma or as high-grade papillary or unclassified carcinoma. Sarcomatoid carcinoma derives from morphological progression of any type of renal cell carcinoma. The group of oncocytomas/chromophobe renal cell carcinomas can be considered as a spectrum from benign (oncocytoma) to malignant neoplasm (chromophobe renal cell carcinoma). They are sometimes encountered in oncocytomatosis or familial Birt-Hogg-Dubbe syndrome in which tumoral cells may have hybrid features. Angiomyolipoma is usually a benign mesenchymatous neoplasm, that can be sporadic or familial (tuberous sclerosis). In the latter situation, some cases of epithelioid angiomyolipoma (potentially malignant) have been described. Renal epithelial and stromal tumors (REST) is a new concept gathering two benign mixed mesenchymal and epithelial tumors: cystic nephroma and mixed epithelial and stromal tumors (MEST).