Currently includes carcinomas that do not have the characteristics of existing renal cell carcinoma subtypes and can be low-grade or high-grade. These include the following types: renal cell carcinoma with pathologic features of more than 1 type of renal cell carcinoma, renal cell carcinoma with mucus secretion, renal cell carcinoma with unclassified epithelial components, low-grade or high-grade unclassified eosinophilic tumors, and sarcomatoid carcinoma. As the understanding of renal cell carcinoma progresses, the proportion of this classification will become smaller and smaller.