Research Article

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 2

Typical expression features of the “three 7” markers in CCRCC (a), RO (e), and PRCC (i), if positive. CK7 (b), CD117 (c), and Claudin-7 (d) show focal and mild-to-moderate positivity in different cases of CCRCC. RO is typically positive for CD117 (g), but for CK7 (f) and Claudin-7 (h), the positive proportion and intensity are usually limited. Focal and moderate positivity for Claudin-7 (l) can be appreciated in PRCC; diffuse and moderate positivity for CK7 (j) is not uncommon, particularly in the type 1 PRCC, but CD117 (k) is generally negative in PRCC (note: mild positivity for Claudin-7 is usually characterized by an incompletely membranous pattern or both membranous and cytoplasmic staining patterns).