Malignant epithelioid angiomyolipoma of the kidney

Angiomyolipoma (AML) is a common benign renal tumor composed of thick-walled blood vessels, smooth muscle, and adipose tissue, but the malignant epithelioid variant is extremely rare. A 78-year-old woman presented with fever and left flank pain for 3 days. Computed tomography showed a heterogeneously enhanced mass without fat density in the left kidney. Radical nephrectomy was performed and pathology showed malignant epithelioid AML with regional lymph node metastases. The tumor cells were positive for human melanosome-associated protein (HMB-45) on immunohistochemical staining. The patient died of disseminated metastases (lungs and bones) 5 months postoperatively. Epithelioid AML is a potentially aggressive tumor. The prognosis is poor in metastatic disease. HMB-45 immunoreactivity is a useful marker to make diagnosis.