Malignant monotypic epithelioid angiomyolipoma of the retroperitoneum.

Monotypic epithelioid angiomyolipoma (EAML) is an uncommon variant of angiomyolipoma, occurring primarily in the kidney and characterized by a predominance of HMB-45-positive epithelioid cells. EAML is generally considered a benign neoplasm, though rare cases exhibiting malignant behavior have been reported. We describe a patient with a primary retroperitoneal monotypic EAML, composed exclusively of atypical epithelioid cells, which metastasized to the liver and the mediastinum. This case represents, to our knowledge, the first description of metastatic disease occurring in an EAML of this particular site.