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Kidney tumor - cysts, children, adult benign

Benign (usually) adult tumors

Mixed epithelial and stromal tumor

Reviewers: Mandolin Ziadie, M.D. (see Reviewers page)
Revised: 10 December 2014, last major update February 2012
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.


● Benign tumor with cystic and solid growth of benign mesenchymal and epithelial elements in ovarian-type stroma, first described in 1998 (Pathol Res Pract 1998;194:445)
● Appears to be same disease but different morphology as cystic nephroma (Am J Surg Pathol 2009;33:72, Am J Surg Pathol 2007;31:489, Arch Pathol Lab Med 2006;130:80)
● Also called cystic hamartoma of renal pelvis (Am J Surg Pathol 1993;17:1169) and adult mesoblastic nephroma (Am J Surg Pathol 1993;17:1029, Am J Surg Pathol 1998;22:827), although it lacks the genetic abnormalities of mesoblastic nephroma (Hum Pathol 2001;32:513)
● Diffuse PAX2 / PAX8 staining of epithelium, coupled with ER- staining, suggests epithelium demonstrates renal tubular differentiation and undergoes architectural and cytologic changes as it grows along with the stromal component (Am J Surg Pathol 2011;35:1264); stroma and epithelium appear to arise from a common cell of origin (Am J Surg Pathol 2011;35:1 114);


● Rare; almost exclusively occurs in perimenopausal women with obesity or receiving exogenous hormones, or men treated with lupron or DES (Am J Surg Pathol 2000;24:958)

Clinical features

● Usually benign; does not recur / metastasize

Case reports

● 41 year old woman #1 (Arch Pathol Lab Med 1990;114:533), #2 in dialysis patient with bilateral tumors 5 years apart (Hum Pathol 2008;39:142)
● 53 year old woman with incidental cystic mass (Mod Pathol 1999;12:417)
● 58 year old man with no history of hormonal treatment (Urology 2008;71:168.e7)
● 72 year old woman (Case of the Week #83)
● Fat predominant tumor resembling angiomyolipoma (Int J Surg Pathol 2008;16:73)
● Two cases with malignant transformation (Hum Pathol 2008;39:463)
● Malignant tumor with rhabdoid differentiation (Hum Pathol 2007;38:1432)


● Nephron-sparing surgery is recommended (Urology 2008;71:1142)

Gross description

● Well circumscribed but unencapsulated tumor in renal pelvis
● Mean 6 cm, range 3-12 cm, solid and cystic and yellow-tan

Gross images


Various images

Multiloculated cystic tumor with smooth cyst lining

Micro description

● Cystic and solid growth of benign mesenchymal and epithelial elements in ovarian-type stroma that contains smooth muscle, fibroblasts and myofibroblasts with embedded epithelial structures (tubules and cysts)
● Cysts often have hobnailed epithelium
● No blastema, no immature epithelial elements and no atypia
Classic: no hemorrhage, no necrosis and no / rare mitotic figures
Cellular: increased stromal cellularity, may have hemorrhage, necrosis and high mitotic index

Micro images

Spindled myofibroblastic stromal component with tubular elements

Various images


Stromal predominant tumor

Case of Week #83

Left to right: AE1/AE3, ER, PR

Positive stains

Epithelium: keratin, EMA, CEA and vimentin
Stroma: alpha smooth muscle actin, desmin, vimentin, ER and PR

Negative stains

● HMB45, CD34
Stromal cells: AE1-AE3, EMA and S100

Electron microscopy description

● Spindle cells have mitochondria, ribosomes and submembranous condensations composed of clusters of filaments
● Also basement membrane, abundant collagen fibers, dense plaques, pinocytotic vesicles and nearly continuous external lamina
● Rare endoplasmic reticulum

Differential diagnosis

Clear cell renal cell carcinoma: more than occasional clear cells
Leiomyoma: particularly stromal predominant tumors (Arch Pathol Lab Med 2005;129:910) - no epithelial elements except trapped normal tissue, no ovarian-type stroma and not cystic
Nephroblastoma / cystic partially differentiated nephroblastoma: blastema present
Metanephric adenoma or adenofibroma: children / young adults, cysts uncommon, spindle cells are actin- and desmin-
Sarcomatoid renal cell carcinoma: atypia, renal cell carcinoma component present, necrosis and mitotic figures
Solitary fibrous tumor: no epithelial elements, no ovarian type stroma and is usually not cystic

End of Kidney tumor - cysts, children, adult benign > Benign (usually) adult tumors > Mixed epithelial and stromal tumor

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