Malignant pigmented clear cell epithelioid tumor of the kidney: Clear cell("sugar") tumor versus malignant melanoma

A 73-year-old woman presented with an hemorrhagic kidney tumor initially in terpreted as a renal cell carcinoma (RCC). A retroperitoneal recurrence inf iltrating the duodenal wall was made up of clear cells, some of which conta ined Fontana-Masson positive pigment, immunopositive for HMB-45, S-100 prot ein, actin, and vimentin. The same immunohistochemical profile was retrospe ctively reproduced in the kidney tumor, where melanosomes were also found u ltrastructurally. Lipomatous differentiation was not observed. There was no history of malignant melanoma (MM), or stigmata of tuberous sclerosis. The patient died of disease 5 years after the initial diagnosis. This neoplasm can be considered as a malignant, pigmented, clear-cell epithelioid varian t of angiomyolipoma, or "sugar" tumor of the kidney, with the peculiarity o f having a previously unreported component of pigmented cells visible on li ght microscopy. This finding raises the possibility that the exceptional ca ses of MM reported in renal parenchyma may be pigmented variants of epithel ioid angiomyolipoma rather than true MM. HUM PATHOL 31:516-519. Copyright ( C) 2000 by W.B. Saunders Company.