[Renal tumors in adults: rare tumors and new tumor entities].

International agreement was reached on the histologic classification of renal epithelial neoplasms during the last years. This classification defines malignant neoplasms as clear-cell (conventional) renal carcinoma, papillary renal carcinoma, chromophobe renal carcinoma, collecting duct carcinoma and renal cell carcinoma, unclassified. Benign neoplasms are papillary adenoma, renal oncocytoma and metanephric nephroadenoma/adenofibroma. Over the past few years, new or rare distinctive kidney tumors have been described. The aim of this review is to present examples of recently recognized clinicopathologic tumor entites and to discuss the value of immunohistochemical and molecular tests for the differential diagnosis. The following tumors will be described: mixed epithelial/stromal renal tumors, primary renal synovial sarcomas, primary renal primitive neuroectodermal tumors, low grade myxoid renal epithelial neoplasms with distal nephron differentiation and epitheloid angiomyolipoma. Detection of SYT-SSX gene fusion transcripts resulting from the t(X;18) and the EWS-FLI-1 gene fusion are described as molecular tests for the diagnosis of renal synovial sarcomas and renal primitive neuroectodermal tumors. Immunohistochemical expression of hormone receptor is helpful to diagnose mixed epithelial/stromal renal tumors. It is important to distinguish these tumor entities from adult Wilms' tumors and sarcomatoid renal cell carcinomas because of a different biological behaviour and different therapeutical approaches.