Renal epithelioid angiomyolipoma with a negative premelanosome marker immunoprofile: a case report and review of the literature

Abstract

Introduction: The rare variant of renal epithelioid/pleomorphic angiomyolipoma has been reported in approximately 120 cases. One of the most important characteristics to differentiate these tumors from other renal cell neoplasms is their typical reactivity to premelanosome antigens. If such a tumor does not stain for HMB-45 or Melan-A, a specific diagnosis of epithelioid pleomorphic angiomyolipoma cannot be made with certainty.

Case presentation: We present here what is, to the best of our knowledge, the first case of epithelioid/pleomorphic angiomyolipoma of the kidney in a 50-year-old Caucasian man with no history of tuberous sclerosis, and with a tumor marker profile negative for several premelanosome antigens. The tumor was composed of sheets of pleomorphic, round to polygonal epithelioid cells with prominent eosinophilic cytoplasm, large nuclei, many multinucleated, and very prominent nucleoli. There were prominent vessels and rare interspersed smooth muscle fibers, but adipocytes were not identified. A tumor marker profile showed tumor cell reactivity for CD68, calponin and focally for CD10. Intervening smooth muscle was reactive with smooth muscle actin. The tumor lacked reactivity for melanin-associated antigens HMB-45 and Melan-A, and for CD31, pan-cytokeratin (AE1/3) and desmin. Electron microscopic examination of tumor cells confirmed the presence of premelanosome-like granules.

Conclusions: Based on the characteristic microscopic appearance of this tumor, and its overall tumor marker profile, we concluded this was a renal epithelioid/pleomorphic angiomyolipoma with a negative premelanosome antigen phenotype.

Figure 1

(A) Computed tomography scan showing a heterogeneous hypo-dense mass in the left kidney measuring 73×66×65mm across its maximal dimensions (crossing yellow bars). A 35mm simple cyst is present in the right kidney. (B) Microscopic image from hematoxylin and eosin sections of the epithelioid variant of angiomyolipoma tumor showing sheets of pleomorphic, round to polygonal epithelioid cells, with prominent eosinophilic cytoplasm, large nuclei, many of them multinucleated, and with very prominent nucleoli; some interspersed smooth muscle fibers were present but no adipocytes were identified (40× objective). Microscopic images from the renal epithelioid angiomyolipoma with immunoperoxidase stainings showing positive reactivity for calponin (C), CD68 (D), smooth muscle actin (E), and negative reactivity for HMB45 (F) (all at 40× objective).

Figure 2

Electron microscopic image of renal epithelioid angiomyolipoma cells bearing cytoplasmic organelles consisting of premelanosomes, similar to those reported previously [6].