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60-year-old man with sudden weight loss
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DiscussionChromophobe RCC Pathophysiology Chromophobe RCC arises from intercalated cells of the renal cortex. Epidemiology It is the third most common subtype of renal cell carcinoma. It comprises 5%-11% of renal epithelial tumors. Mean age is 59 years and men are affected more than women. Clinical presentation Most patients are asymptomatic, and a unilateral tumor is found incidentally on imaging. Chromophobe RCC is associated with Birt-Hogg-Dube syndrome. Grossly, the tumor is circumscribed, light brown, and may have a central scar. Microscopic features Classic tumors are composed of large cells with an abundant pale cytoplasm with prominent cell borders. Binucleation is common. The pattern of growth is predominantly solid, separated by thin, incomplete fibrovascular septa. In the classic type, the predominant cell type has a pale, clear-appearing cytoplasm. The eosinophilic variant is composed of cells with an abundant granular, eosinophilic cytoplasm. Hale’s colloidal iron shows diffuse staining in the cytoplasm. The most characteristic feature is hyperchromatic nuclei showing irregular wrinkled outlines with perinuclear halos. Most tumors are positive for CK 7, CD117, and E-Cadherin. Ultrastructurally, the cells contain abundant microvesicles and degenerating mitochondria. Prognostic and molecular features Prognosis is determined by tumor size, small-vessel invasion, presence of necrosis, and sarcomatoid change. Sarcomatoid features (2%-8% of cases) and perinephric extension are associated with aggressive behavior. Grading is not recommended due to a lack of association with outcome. There can be loss of multiple chromosomes including 1, 6, 10, 13, 17, and 21. TP53 mutations are seen in 20%-32% of cases and PTEN mutations are seen in 6%-9%. References
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