9 May 2007 – Case of the Week #83
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Case of the Week #83
A 72 year old woman presented with gross hematuria. She had a 2.5 cm enhancing mass in the left renal pelvis on CT. A left nephrectomy was performed
What is your diagnosis?
Mixed Epithelial and Stromal Tumor of Kidney
Mixed epithelial and stromal tumor of the kidney is a rare, benign tumor, almost exclusively in perimenopausal women with obesity or receiving exogenous hormones, or in men treated with lupron or DES (AJSP 2000;24:958). It is also called cystic hamartoma of the renal pelvis, and previously was called adult mesoblastic nephroma, although it lacks the genetic abnormalities of congenital mesoblastic nephroma (Hum Path 2001;32:513)
It usually occurs in the renal pelvis as a well circumscribed but unencapsulated yellow-tan tumor with solid and cystic components and a mean diameter of 6 cm. Microscopically, there are benign epithelial tubules and cysts in ovarian-type stroma that contains smooth muscle, fibroblasts and myofibroblasts. Cysts often have hobnail epithelium. There is no blastema, no immature epithelial elements and no atypia. Typically, there is no hemorrhage, necrosis or mitotic activity.
The epithelial component is immunoreactive for broad spectrum cytokeratins (AE1-AE3), EMA, CEA and vimentin. The stroma is positive for smooth muscle actin, desmin and vimentin as well as estrogen and progesterone receptors.
These tumors have benign behavior, with no recurrences of metastases.
Recent reports suggest that mixed epithelial and stromal tumor may be related to cystic nephroma, due to similar demographics (middle-aged women), predominance of cysts lined by hobnail cells, ovarian-type stroma, lack of atypia and benign behavior (AJSP 2007;31:489, Ann Diagn Pathol 2006;10:77, Archives 2006;130:80). However, mixed epithelial and stromal tumors do not occur in men, are more often immunoreactive for ER and PR, have higher stromal ratios and more frequent ovarian-type stroma, and often lack large cysts.
The differential diagnosis may be broad, depending on the relative amounts of various components present. It includes Wilm’s tumor (blastema present), metanephric fibroma (children and young adults, no cysts, stroma is negative for actin and desmin), clear cell carcinoma (has more than occasional clear cells), and sarcomatoid renal cell carcinoma (prominent atypia, necrosis and mitotic figures).
Nat Pernick, M.D., President
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