Mixed epithelial and stromal tumor (MEST) is a biphasic tumor of the kidney seen almost exclusively in middle-aged or older females. Like multicystic nephroma, it is a well-circumscribed tumor usually located close to the hilum and renal pelvis. It is composed of small and large cysts and may have solid areas. It cannot be distinguished grossly from multicystic nephroma. There are histologic features that favor the diagnosis of MEST over multicystic nephroma which are discussed in subsequent images. Steroid hormones are considered to play an important role in the pathogenesis of MEST as supported by the frequent expression of estrogen and progesterone receptors in the stromal component. Image copyright: pathorama.ch.