Fat-predominant mixed epithelial stromal tumor (MEST): Report of a unique case mimicking angiomyolipoma

A unique case of a mixed epithelial stromal tumor (MEST) that was predominantly composed of adipose tissue is reported here. Radiographically and grossly, the lesion was thought to be an angiomyolipoma, based upon its fatty appearance. Microscopically, the lesion was predominantly composed of mature adipose tissue but also contained clusters of bland tubules surrounded by smooth muscle bundles and collagen. By immunohistochemistry, the stroma labeled diffusely for estrogen and progesterone receptors, while the muscle bundles labeled for desmin. Melanocytic markers HMB45 and Melan A, typically positive in angiomyolipoma, were nonreactive. This case expands the morphologic spectrum of MEST to include mimics of angiomyolipoma.