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Chromophobe renal cell carcinoma (RCC) is a distinct type of renal cell carcinoma, characterized by large pale cells with prominent cell membranes. In some cases distinction between chromophobe RCC and conventional RCC in routine light microscopy remains problematic. Electron microscopy has been of value because cytoarchitectural features of tumor cells are emphasized in the current classification of renal epithelial tumors. We analyzed the ultrastructural features of five cases of clear cell RCC and three cases of chromphobe RCC. Under light microscope, chromophobe RCC was composed of solid sheets of cells with reticular cytoplasm, perinuclear clearing, and prominent cell borders. Their nuclei were slightly enlarged and pleomorphic with visible nucleoli, estimated as Fuhrman nuclear grade 2 in all cases. Chromophobe RCC showed many cytoplasmic vesicles, ranging from 150-300 nm in diameter. In addition, abundant mitochondria, and short and stubby microvilli are noted. Some of cytoplasmic vesicles were dilated, with additional vesicles within them. The mitochondria showed distinct abnormalities, including outer membrane outpouching and abundant tubulovesicular cristae. Glycogen pools and lipid droplets are not noted. General ultrastructural features of clear cell RCC were long microvilli similar to the brush border of the normal proximal tubules, with abundant cytoplasmic lipid and glycogen. Basal lamina and junctional complex was not prominent in two cases, possibly due to delayed fixation. In one case, large electron dense granular globular structures were present in the cytoplasm. These ultrastructural features of chromophobe RCC and clear cell RCC were consistent with the findings previously described. Electron microscopy has pivotal role in diagnosis and histogenesis of renal epithelial tumors. However, in tumors with heterogenous cell population, sampling should be done in many areas.
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