Oncocytoma versus chromophobe renal cell carcinoma. Is there something in between?

The differentiation of oncocytic tumors of the kidneys is often difficult, particularly in renal biopsies. Differential diagnoses are chromophobe renal cell carcinoma (ChRCC), renal oncocytoma (RO), the oncocytic variant of papillary renal cell carcinoma (OPRCC), the eosinophilic variant of clear cell renal cell carcinoma (CCRCC) and hybrid oncocytic chromophobe tumors (HOCT). In difficult cases that cannot be resolved by morphology alone, immunohistochemistry is usually helpful. The RO and ChRCC show positive reactions for CD117, they are negative for vimentin and alpha-methylacyl-CoA racemase (AMACR), while CCRCC are positive for vimentin and OPRCC are positive for AMACR. To distinguish between RO and ChRCC, CK7, claudin-7 (both strongly positive in ChRCC and negative or patchy positive in RO) and epithelial cell adhesion molecule (EpCAM) can be used (positive in ChRCC, negative in RO); however, a diagnosis may remain difficult in some cases even with the use of immunohistochemistry. Thus, numerous new methods are being developed in the field of molecular pathology and computer-based morphometric tumor analysis; however, these new methods have not yet been applied in routine diagnostics.