Mesenchymal Kidney Tumors

Mesenchymal tumors involving the kidney include a wide range of benign and malignant tumors and are relatively rare compared to epithelial neoplasms. Within the last two decades, there have been major discoveries in the underlying genomic alterations that drive the neoplastic process in mesenchymal lesions of the kidney. Specifically, a variety of translocation-associated sarcomas have been described arising from the kidney, significantly expanding the differential diagnosis of mesenchymal tumors primary to the kidney. This chapter is devoted to the clinical, morphologic, immunohistochemical, and genomic alterations of mesenchymal tumors that primarily occur in adults, with discussion of the differential diagnosis of specific entities. In contrast to the childhood lesions, most of these entities occur primarily in somatic soft tissue sites, but are also described in the kidney and constitute an ever-increasing list that appear to have a predilection for this location. It must be recognized that many of the neoplasms reviewed also occur in children.