Combined Immunohistochemistry for the “Three 7” Markers (CK7, CD117, and Claudin-7) Is Useful in the Diagnosis of Chromophobe Renal Cell Carcinoma and for the Exclusion of Mimics: Diagnostic Experience from a Single Institution

Figure 3

Examples for combining FISH and the “three 7” markers to confirm the diagnosis in a small subset of difficult cases. A case of CHRCC-like CCRCC (a) displays predominantly solid sheets of polygonal cells with clear to finely eosinophilic cytoplasm, a distinct membrane, and slight nuclear irregularity, mimicking CHRCC, with focal areas showing nests of clear cells with a completely delicate vascular configuration, corresponding to the morphology of CCRCC (inset of (a)); negativity for all “three 7” markers, in this case, is useless, but FISH showing the loss of 3p (b) (green signal: CSP3; red signal: 3p) facilitates a correct diagnosis in this scenario. A solid type PRCC (c) here does not show a distinct histomorphology and may occasionally mimic CHRCC or CCRCC. This rare case, only showing positivity for CK7 and focal CD117 staining (not shown), may represent a diagnostic dilemma, but FISH showing the existence of CEP7 and CEP17 trisomy (d) (green signal: CEP 7; red signal: CEP 17) without the loss of 3p contributes to the final diagnosis.

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