Subtypes of chromophobe cell renal carcinoma: an ultrastructural and histochemical study of 13 cases

The Mainz classification of renal epithelial neoplasms has become accepted as a reproducible morphologic and cytogenetic classification of epithelial tumors of the kidney. Chromophobe cell renal carcinoma (CCRC) is a distinct type of renal epithelial neoplasm, first described by Thoenes et al. in 1985. Both a typical type of CCRC, composed of cells with pale reticular cytoplasm, and an eosinophilic variant (EVCCRC) have been identified. Both variants have been reported to show cytoplasmic staining with the Hale's colloidal iron method. Cytogenetic analysis has tended to confirm the Mainz classification. CCRC has been shown to have consistent chromosomal abnormalities that are not shared by other renal tumors. Ultrastructurally, CCRC is typically characterized by a cytoplasm containing scant numbers of mitochondria, which have tubulovesicular christae, and by the presence of innumerable 150-300-microm microvesicles scattered between the mitochondria. Erlandson et al. recently described two subtypes of EVCCRC. One subtype has sparse microvesicles and abundant mitochondria that have tubulovesicular christae, whereas the second type (described as an oncocytic EVCCRC) has no microvesicles and abundant mitochondria containing pseudovesicular or lamellar christae. This was believed to be more akin to the ultrastructural appearances of a renal oncocytoma. The authors believe that the phenotype of the EVCCRC shows a range of appearances at both the light microscopic and the ultrastructural levels, from features similar to the typical type CCRC through to a neoplasm that is phenotypically similar to renal oncocytoma. A series of 13 cases of CCRC from the files of the Massachusetts General Hospital for which ultrastructural examination was available is described. These cases include six cases of typical type CCRC and seven cases of EVCCRC. The authors confirm the findings of Erlandson et al. of two subtypes of EVCCRC and designate them as type 1 EVCCRC (with some microvesicles and mitochondria with tubulovesicular christae) and type 2 EVCCRC (with no identifiable microvesicles and mitochondria with pseudovesicular or lamellar christae).