• macroscopic hematuria;
  • neoplasm;
  • sarcoma

We describe a novel cystic renal tumor consisting of benign epithelial and malignant stromal components in a 56-year-old woman who was admitted to hospital with macroscopic hematuria. Enhanced computed tomography revealed a multilocular 3.4 × 2.7-cm tumor in the center of the left kidney. After total left nephrectomy, the excised tumor appeared extensively cystic with a well defined border on the cut surface. Histologically, the tumor was composed of biphasic a benign epithelial lining on tubules or cysts with a typically hobnailed appearance, and anaplastic sarcomatous stroma with frequent mitosis. Periepithelial cuffing of the sarcoma cells was evident without an epithelial-stromal transition. Carcinomatous nests, blastemic elements, ovarian-like stroma or differentiated mesenchyme were not evident in the stroma. The epithelial cells were reactive with cytokeratins, epithelial membrane antigen (EMA), vimentin and transducin-like enhancer protein 1 (TLE1). Stromal cells were reactive with vimentin, CD99 and TLE1, partly reactive with CD34 and CD10, and non-reactive with cytokeratins, EMA, Wilm's tumor protein (WT-1), estrogen receptor (ER), progesterone receptor (PgR), CD57, HMB45 or Bcl2. SYT-SSX fusion gene was not detected with reverse transcription polymerase chain reaction. Because these findings did not coincide with established descriptions of cystic renal neoplasms, we preferred the term, ‘adenosarcoma’. This could become a new classification for adult cystic renal tumors.