[About a rare tumor of the kidney: Malignant mixed epithelial and stromal tumor].

Mixed epithelial and stromal tumor of the kidney is a recently described neoplasm that predominantly affects perimenopausal women. Few cases with malignant features have been reported. Here, we report the case of malignant mixed epithelial and stromal tumor of the kidney with sarcomatous transformation arising in a 27-year-old female. She presented with abdominal discomfort. Computed tomography of the abdomen revealed a large compressive mass arisen from the left kidney with solid and focal cystic components. The patient underwent left radical nephrectomy. Histologic sections showed benign and malignant components. The benign component consisted of multiple tubules and variably sized cysts lined by benign epithelium. The malignant component was composed of undifferentiated cellular spindle cell sarcoma. By immunohistochemical studies, the epithelial component was positive for cytokeratins and epithelial membrane antigen (EMA). The stromal component displayed strong immunohistochemical expression of vimentin, CD99, bcl2; and was negative for cytokeratins, desmin, SMA, S-100, estrogen receptor (ER) and progesterone receptor (PR). Analysis by reverse transcriptase polymerase chain reaction (RT-PCR) failed to identify the SYT-SSX1 or SYT-SSX2 fusion transcripts characteristic of synovial sarcoma.