Mixed Epithelial & Stromal Tumor
The cysts are lined by flattened tubular epithelium. The cyst walls have hypercellular spindled stroma with resemblance to ovarian stroma. Frequently, the stromal component expresses estrogen and progesterone receptors indicating the role of steroid hormones in the pathogenesis of this tumor. The tumor is sharply demarcated from the normal kidney on the left.