Malignant clear cell "sugar" tumor of the kidney: clear cell variant of epithelioid angiomyolipoma.

Abstract

Angiomyolipoma is a heterogeneous proliferation composed of an admixture of blood vessels, smooth muscle cells, adipocytes and peculiar myoid cells with variable melanin synthesis. Epithelioid angiomyolipoma, which often has malignant potential, has been reported previously.1 Recently clear cell “sugar” tumor has been described as a clear cell variant of epithelioid angiomyolipoma.2 Clear cell “sugar” tumor or epithelioid angiomyolipoma of the kidney is microscopically similar to renal cell carcinoma and, therefore, differential diagnosis is often difficult.2 However, the habitual presence of melanosomes in these lesions is significant and distinguishes them from renal cell carcinoma.1 We report a case of clear cell “sugar” tumor that consisted of pigmented clear cells resembling renal cell carcinoma. CASE REPORT A 23-year-old woman presented with left abdominal pain. The patient had no history of tuberous sclerosis. Ultrasonography and computerized tomography demonstrated a 10 9 cm. tumor in the left kidney and retroperitoneal lymph node swelling (fig. 1). Left nephrectomy and retroperitoneal lymph node dissection were performed. Macroscopic finding was an expansive tan colored renal tumor. The tumor was made up of clear cells with scattered sarcomatoid features, and some cells contained intracytoplasmic brown pigment. Immunohistochemically the expression of HMB-45, melanosome associated protein, was positive although other immunostains, including epithelial markers (epithelial membranous antigen and cytokeratin), vimentin and S-100, were negative (fig. 2). The melanosomes were detected via electron microscopy.