Oncocytoma-like angiomyolipoma: A clinicopathologic and immunohistochemical study of 2 cases

Archives of Pathology & Laboratory Medicine,  May 2002  by Martignoni, Guido,  Pea, Maurizo,  Bonetti, Franco,  Brunelli, Matteo,  Eble, John N

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* We report the clinical, pathologic, and immunohistochemical features of an unusual tumor of the kidney composed of densely eosinophilic, polygonal epithelioid cells. The patients were a 56-year-old woman and a 35-year-old man. The renal tumors were discovered during follow-up for breast carcinoma and evaluation for abdominal pain, respectively. The tumors closely resembled oncocytoma in routine sections, but were negative for epithelial markers and positive for HMB-45, a pattern of reactions characteristic of angiomyolipoma. In the woman, a single additional microscopic angiomyolipoma was present in the renal parenchyma at a distance from the main tumor. Both patients are alive without recurrence 7 and 10 years after surgery, respectively. Based on clinical, morphologic, and immunophenotypic features, we conclude that these tumors are oncocytoma-like angiomyolipomas.

(Arch Pathol Lab Med. 2002;126:610-612)

Incocytoma is a renal epithelial neoplasm composed of polygonal cells with abundant, finely granular, eosinophilic cytoplasm filled with densely packed mitochondria. Typical architectural patterns include sheets, islands, and tubules.1-3 Immunohistochemical studies have confirmed the epithelial nature of renal oncocytoma, showing the expression of a variety of epithelial markers and the absence of vimentin.4 Hundreds of oncocytomas have been studied during the past 25 years, and it is clear that oncocytoma is benign.5

In this study, we report the clinical, pathologic, and immunohistochemical features of 2 unusual angiomyolipomas of the kidney composed of densely eosinophilic epithelioid cells resembling oncocytoma.

REPORT OF CASES

Case 1

This 56-year-old woman was seen in routine follow-up for breast carcinoma, which had been resected 5 years earlier. A sonogram showed a 25-mm tumor in the lateral aspect of the right kidney. Surgical enucleation was performed. During this surgical procedure, an additional 5-mm subcapsular nodule was found and removed. Subsequently, the patient was evaluated for cutaneous and neurological findings of tuberous sclerosis, and none was found. Seven years later, the patient is well and without recurrence.

Case 2

A 35-year-old man presented with abdominal pain. Radiographic evaluation revealed a 50-mm renal tumor. Nephrectomy was performed. The patient was evaluated for cutaneous and neurological findings of tuberous sclerosis, and none was found. Ten years later, the patient is well and without recurrence.

MATERIALS AND METHODS

The 2 cases we describe are from the files of the Dipartimento di Patologia-Sezione Anatomia Patologica dell' Universita' di Verona, Verona, Italy. Tissue specimens were fixed in formalin (10%) for 24 to 48 hours and routinely processed for paraffin embedding. The original sections were examined, and new sections were prepared from the blocks and stained with hematoxylin-eosin, periodic acid-Schiff (with and without diastase), and immunohistochemically with the avidin-biotin method and a panel of antibodies recognizing the following molecules: vimentin (Amersham, Buckinghamshire, England; dilution 1:10), cytokeratin AEl/AE3 (Boehringer, Mannheim, Germany; 1:500), cytokeratin CAM5.2 (Becton Dickinson, Mountain View, Calif; 1:10), epithelial membrane antigen (Dakopatts, Glostrup, Denmark; 1: 50), chromogranin (Enzo Diagnostics, New York, NY; 1:10), HMB-45 (gp100 protein; Dakopatts; 1:40), S100 protein (Dakopatts; 1:500), desmin (D33; Dakopatts; 1:500), and smooth muscle actin (1A4; Dakopatts; 1:100).

Ten oncocytomas and 30 angiomyolipomas from the files of the Dipartimento di Patologia-Sezione Anatomia Patologica dell' Universita' di Verona were compared with the study tumors.

PATHOLOGIC FINDINGS

Gross Pathology

The tumors were well circumscribed, approximately spherical, and 25 mm (case 1, Figure 1) and 50 mm (case 2) in diameter. Their cut surfaces were homogeneous, glistening, and tan.

Microscopic Pathology

The 2 tumors were histologically similar. The tumors were composed of sheets of densely packed, mediumsized and large, deeply eosinophilic cells (Figure 2, A). Neither tumor had a fibrous pseudocapsule. The neoplastic cells had regular polygonal contours and resembled epithelial cells (Figure 2, B). No glandular architecture was present. The neoplastic cells had single, nearly spherical nuclei with single central nucleoli (Figure 2, C). Occasional nuclei contained eosinophilic cytoplasmic pseudoinclusions. Mitotic figures were rare. Necrosis was absent. Neither fascicles of smooth muscle cells nor thick-walled tortuous blood vessels were present. Fat cells were not present in the tumors. In the tumor of case 1, a 5-mm synchronous subcapsular angiomyolipoma also was present.

Immunohistochemical Findings

Immunohistochemical results were the same for both tumors. Approximately 10% of their cells had strong cytoplasmic immunoreactivity for HMB-45 (gp100 protein) (Figure 2, D and E). In the tumor of case 1, the reaction with antibody to smooth muscle actin showed focal staining at the cytoplasmic membrane (Figure 2, F). Reactions with antibodies to vimentin, desmin, and 5100 protein were negative. Reactions with antibodies to epithelial markers (AEl/AE3, CAM5.2 [Figure 2, G], and epithelial membrane antigen) were negative in the tumor cells and strongly positive in nearby normal renal parenchyma.