Non-clear cell renal cell carcinoma, part 1: histology.

Non-clear cell renal cell carcinomas (RCCs) represent up to 20% of all RCCs. Despite often being clustered as a single entity, these tumors represent a heterogeneous group of diseases with distinct molecular drivers, histologies, and clinical outcomes. Their low incidence and heterogeneity have resulted in a lack of studies that address the optimal strategies for each subtype. This article (the first in a 2-part series) reviews the histology of RCC, whereas the second article reviews current targeted therapies approved for RCC, such as the vascular endothelial growth factor receptor tyrosine kinase inhibitors and the mammalian target of rapamycin inhibitors. Ongoing studies will provide more information regarding the role of these agents in non-clear cell RCC.