We report a case of a morphologically unusual
renal cell carcinoma with features of both chromophobe and
papillary carcinoma. 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. Specifically, the chromophobe
tumor cells expressed CK7 and c-Kit weakly, while HMWCK, CK19, and AMACR were not detectable. In contrast, the papillary
tumor cells expressed uniformly HMWCK, CK7, and c-Kit and focally CK19 and AMACR. Fluorescence in situ hybridization analysis of nuclei isolated from
paraffin-embedded
tumor tissue detected
monosomy 1, disomy 7, and
monosomy 17, a common and characteristic finding in chromophobe
carcinomas, in a majority of, but not all
tumor cells, whereas a population characterized by disomy 1,
trisomy 7, and trisomy 17, a frequent finding in
papillary carcinoma, was not identifiable. Electron microscopic analysis revealed numerous characteristic small cytoplasmic vesicles in the chromophobe areas, which were absent in the papillary component. This case illustrates the rare coexistence of two distinct and admixed histologic types of
renal cell carcinoma.