1. ¹Department of Pathology and Laboratory Medicine, University of Texas—Houston Medical School, Houston, Texas
2. ²Department of Pathology and Laboratory Medicine, Baylor College of Medicine, Houston, Texas
3. ³Department of Pathology, St. Luke's Episcopal Hospital, Houston, Texas

Correspondence: Sang Ling Wu, M.D., Department of Pathology and Laboratory Medicine, University of Texas—Houston Medical School, 6431 Fannin Street, Houston, TX 77030. e-mail: sang.ling.wu@uth.tmc.edu; fax: 713-500-0730

Accepted 22 March 2002.

Abstract

Chromophobe renal cell carcinomas and renal oncocytomas share morphologic similarities and may present a diagnostic challenge on routine hematoxylin–eosin staining. Currently recommended additional studies of Hale's colloidal iron staining and electron microscopy are often difficult to interpret and technically challenging and may not be readily available. Previous studies have reported conflicting results with regard to the cytokeratin 7 staining pattern in chromophobe renal cell carcinomas and renal oncocytomas. Cytokeratin 20 expression in chromophobe renal cell carcinomas has not pre-viously been studied.

Formalin-fixed paraffin-embedded tissue of 11 chromophobe renal cell carcinomas and 21 renal oncocytomas were retrieved from the archived files (1984–2000) of four teaching hospitals. Of the 11 chromophobe renal cell carcinomas, eight stained positive (73%) for cytokeratin 7, one stained focally positive (9%), and two cases (18%) were completely negative. Cytokeratin 7 staining of the 21 oncocytomas revealed 4 positive (19%), 7 focally positive (33%), and 10 negative cases (48%). Cytokeratin 20 was uniformly negative on all 11 cases of chromophobe renal cell carcinomas and all 21 cases of oncocytomas.

Cytokeratin 7 does not appear to show the consistent immunoreactivity in chromophobe renal cell carcinomas and renal oncocytomas, as has been previously suggested. Cytokeratin 20 immunostaining in chromophobe renal cell carcinomas and renal oncocytomas is uniformly negative. Despite the technical and interpretive challenges of Hale's colloidal iron, it is still the most useful stain in differentiating chromophobe renal cell carcinomas from renal oncocytomas.