Why is sarcomatoid renal cell carcinoma not an independent subtype? What is the clinical significance of unclassified renal cell carcinoma?

Abstract

The term sarcomatoid carcinoma was coined during the late 1960s by Farrow et al. to describe renal carcinomas in which cells have lost epithelial features and have assumed a sarcomatous, or “sarcomatoid,” appearance. The definition was based strictly on the appearance in H&E-stained sections. Thus, it is probable that sarcomatoid components are either sarcoma-like epithelial components or nonepithelial malignant components, such as osteogenic sarcoma or hemangiopericytoma. Strictly defined, it is a carcinoma with sarcoma-like, but epithelial, components as proved by ultrastructural or immunohistochemical studies. Thus, in each case, areas of the usual RCC should be recognized. In practice, however, malignant components could drift away from the epithelial type to the nonepithelial type. Such cases then should be designated carcinosarcoma, mixed carcinoma, or sarcoma. However, because the outcome of such patients is the same as that for patients with tumors having sarcomatoid differentiation, the distinction is more or less academic.