Malignant Mixed Epithelial and Stromal Tumor of the Kidney: Report of a Carcinosarcoma Case and an Updated Literature Review.

Mixed epithelial and stromal tumors of the kidney (MESTK) are rare and recently defined entities that comprise both epithelial and stromal cells. MESTK is mostly benign; however, to date, 18 borderline or malignant cases have been reported. In this study, we report a case of carcinosarcoma exhibiting a large carcinoma and small sarcoma component, and review the relevant literature. The patient was a 59-year-old woman who presented with a large mass in the left kidney having solid and focal cystic components. The patient underwent left radical nephrectomy. The tumor was gray-white and solid-cystic, with a relatively clear boundary. Microscopically, the tumor revealed benign and malignant components. The benign component consisted of multiple tubules, variable-sized cysts lined with benign epithelium, and hyalinized stroma. The malignant component was composed of predominantly small cell neuroendocrine carcinoma and a small quantity of adenocarcinoma, squamous cell carcinoma, and sarcoma. Finally, a diagnosis of the malignant MESTK was made. Certain cases of borderline or malignant transformation of MESTK have been published, so it is important to enhance findings made by other studies.