Objective: Chromophobe renal cell carcinoma is a relatively uncommon variant of renal carcinoma described in 1985. The main differential diagnosis is renal oncocytoma. Hale's colloidal iron staining is a powerful adjunct to morphological interpretation but it is not specific and is sometimes difficult to interpret. We studied the immunohistochemical expression of cytokeratin 7 to determine its value in distinguishing chromophobe renal cell carcinoma from renal oncocytoma.
Methods: Immunostaining was performed on paraffin-embedded tumor tissue of 6 chromophobe renal cell carcinomas and 11 oncocytomas with an antibody to cytokeratin 7 (clone OV-TL 12/30, Dako, France) using a streptavidin-biotin method.
Results: All chromophobe renal cell carcinomas showed strong cytoplasmic staining with peripheral cell accentuation. In contrast, 8 of 11 oncocytomas were entirely negative and 3 showed only weak and focal staining in less than 5% of the tumor cells.
Conclusion: Immunohistochemical staining for cytokeratin 7 may be useful for the differential diagnosis of renal oncocytomas and chromophobe renal cell carcinomas when Hale's colloidal iron staining is uncertain.