Successful treatment with sirolimus for an angiomyolipoma mimicking renal cell carcinoma in a transplanted kidney.

Angiomyolipoma (AML) is a benign mesenchymal tumor composed of blood vessels, smooth muscle, and mature adipose tissue. AMLs in the kidney allografts are rare. We report a case of AML that was incidentally found 1 year after transplantation. Abdominal computed tomography showed a 4-cm renal tumor with contrast enhancement and an early washout pattern, resembling a renal cell carcinoma. Tumor biopsy proved a lipid-poor AML. Tumor diameter decreased to 2.4 cm after 6 months of treatment with sirolimus. Sirolimus not only reduces tumor size, but also benefits a transplant patient who needs immunosuppression.