High power view of a septum between cysts of mixed epithelial and stromal tumor (MEST) of the kidney. It contains an abortive tubule surrounded by ovarian-type stroma and is lined on either side by flattened epithelium. The prognosis of MEST is excellent. Most cases are cured by nephrectomy. There are rare case reports of malignant transformation which may occur in either the mesenchymal (stromal) or the epithelial component.