These have been noted to have fibromuscular stroma and cytokeratin 7 reactivity; however, absence of these genetic alterations in renal cell carcinomas with smooth muscle stroma suggests that this represents only one of likely several entities.
Among the most common useful stains are cytokeratin 7 (separating clear cell RCC [negative] from papillary RCC, clear cell papillary RCC, and multilocular cystic RCC [positive] as well as separating chromophobe RCC [diffusely positive] from oncocytoma [focally positive/negative]) and CD117 (separating chromophobe RCC and oncocytoma [positive] from granular variants of clear cell RCC [negative]).
Diffuse labeling for CK7 can uncommonly be observed in clear cell renal cell carcinomas confirmed to have chromosome 3p loss, although these do not exhibit the expected staining pattern of clear cell papillary renal cell carcinoma, including positivity for CD10 and AMACR.
In low-grade nonpapillary eosinophilic neoplasms, distinction between oncocytoma and low-grade RCC mostly rests on histomorphology; however, cytokeratin 7 immunostain may be helpful.
We observed a good overall stability between primary RCC and corresponding xenografted RCC at P1 and P5 regarding histopathology and immunohistochemistry except for cytokeratin 7 (one case) and p53 (one case) expression.
Immunohistochemical analysis of high molecular weight cytokeratins (HMWCK), cytokeratin 7 (CK7), cytokeratin 19 (CK19), c-Kit, and alpha-methylacyl-CoA racemase (AMACR) demonstrated differential profiles for the two components of the tumor, consistent with the respective patterns commonly observed for pure chromophobe and papillary renal cell carcinomas.
Panels of immunohistochemical stains are proposed for different settings, including renal cell carcinoma (RCC) marker, CD10, and vimentin to suggest renal origin of a metastatic tumor, and markers to aid in subclassification of RCC, including parvalbumin and c-kit for chromophobe RCC, and cytokeratin 7 and alpha-methyl-acyl-CoA racemase for papillary RCC.
Cytokeratin 7 was rarely seen in clear cell renal cell carcinomas, type 2 papillary renal cell carcinomas, and oncocytomas, but was found in the majority of type 1 papillary renal cell carcinomas (97.1%) and chromophobe renal cell carcinomas (88%).