[Epithelioid angiomyolipoma of kidney: clinicopathologic study of two cases and review of literature].

Objective: To study the histopathologic features, differential diagnosis and prognosis of epithelioid angiomyolipoma (EAML) of kidney.
Methods: Two cases of EAML (including one case with recurrence) of kidney were retrieved from the archival files of Departments of Pathology, Navy General Hospital of PLA and Health Science Center of Peking University. The clinicopathologic features, immunohistochemistry, ultrastructural findings and follow-up data were studied and literature reviewed.
Results: Histologically, the tumors were predominantly composed of epithelioid cells with marked cellular pleomorphism. Focal perivascular arrangement was seen. Hemorrhage and necrosis were present and tumor emboli were found in the venous structures. The renal hilar lymph nodes were also involved by tumor cells. Immunohistochemical study showed that the tumor cells (including those in the hilar lymph nodes) were strongly and diffusely positive for HMB45, smooth muscle actin, neuron-specific enolase and vimentin. They were focally positive for S-100 protein, melan-pan and CD68. The staining for epithelial membrane antigen, AE1/3, CK7, CD117, muscle-specific actin, desmin, leukocyte common antigen, CD20, CD45RO, CD30, CD15, chromogranin A, synaptophysin, bcl-2, estrogen receptor, progesterone receptor and p53 were negative. Ultrastructural examination revealed the presence of melanosome-like dense granules, myofilaments and dense bodies in the tumor cell cytoplasm. Discontinuous and focally thickened basal lamina was seen surrounding the tumor cells. On follow up, both patients remained well and disease-free 10 months after operation.
Conclusions: EAML is predominantly or almost entirely composed of epithelioid cells. Perivascular cellular arrangement, focal features of otherwise classic angiomyolipoma, as well as coexpression of HMB-45 and smooth muscle actin are clues to the correct diagnosis. The degree of cytologic atypia, presence of hemorrhage and necrosis and high mitotic activity may indicate the malignant potential of this tumor. On the other hand, the presence of lymph node involvement and even tumor emboli in renal veins may represent multifocaltumorigenicity rather than true malignancy. Definitive evidence of malignancy requires demonstration of distant metastasis.