Malignant mixed epithelial and stromal tumor of the kidney: the second male case and review of literature.

Mixed epithelial and stromal tumor of the kidney is a recently described neoplasm that predominantly affects perimenopausal women. Although typically benign, few cases with malignant features have been reported. Here, we report the second male case of malignant mixed epithelial and stromal tumor of the kidney with sarcomatous transformation. The patient presented with abdominal discomfort and right flank pain. Computed tomography (CT) of the abdomen revealed a large mass arisen from the right kidney with solid and focal cystic components. The patient underwent right 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 predominantly 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, CD-99, bcl-2; 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. Subsequently adjuvant chemotherapy was given. The patient developed a local recurrent tumor 9 months after operation.