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This is a rare neoplasm of the childhood kidney with a mean age of 2 yrs. These tumors present with an abdominal mass revealing a tumor arising within the renal medulla with smooth walled cysts. The average size of the tumor was 5.5 cm. These tumors were all treated with surgical excision and none experienced recurrence or metastasis.

Stromal tumors of the kidney comprise about 15% of pediatric renal neoplasms. Wilm's tumor comprises the majority of the pediatric kidney tumors. The importance in making the correct diagnosis in this case lies in differentiating this tumor from other stromal tumors. It is currently hypothesized that these tumors are related to Wilm's tumor. Although no tumor has behaved aggressively, longer follow-up and accumulation of additional cases is needed.


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GENERAL Scalloped subtly infiltrative border
Nodular low power architecture
Prominent vasculature
May have focally high mitotic rate
CD34+, S100+

Metanephric Stromal Tumor Report of 31 Cases of a Distinctive Pediatric Renal Neoplasm

Pedram Argani, M.D.; J. Bruce Beckwith, M.D.

From the Department of Pathology, The Johns Hopkins Hospital, Baltimore, Maryland, U.S.A. (P.A.); the Department of Pathology, Loma Linda University School of Medicine, Loma Linda, California, U.S.A. (J.B.B.); and the National Wilms Tumor Study Group Pathology Center.

Am J Surg Pathol 2000;24:917-926 Abstract quote

We report 31 cases of a novel pediatric renal neoplasm, metanephric stromal tumor (MST).

Mean patient age was 2 years, and the most common presentation was that of an abdominal mass. Gross examination typically revealed a fibrous lesion centered in the renal medulla containing smooth-walled cysts (mean tumor size, 5.5 cm). MST is histologically identical to the stromal component of metanephric adenofibroma (MAF, previously termed nephrogenic adenofibroma) and is an unencapsulated spindle cell lesion that entraps native kidney.

Characteristic histologic features of MST include alternating cellularity that imparts a nodular low-power appearance, onion-skin cuffing around entrapped renal tubules, heterologous differentiation (glia or cartilage), and vascular alterations (angiodysplasia of entrapped arterioles, juxtaglomerular cell hyperplasia in entrapped glomeruli). Three tumors in which the vascular alterations were particularly florid were associated with extrarenal vasculopathy and attendant morbidity. A majority of cases stained for CD34, although the degree of staining was variable. Most patients were treated with surgical excision alone, and none experienced recurrence or metastasis.

Recognition of this entity can spare a child potentially toxic adjuvant chemotherapy that might be used for lesions in its differential diagnosis, specifically clear cell sarcoma of the kidney.

Clear Cell Sarcoma of the Kidney Negative for CD34 and S-100
Regular branching capillary vasculature



Mixed Epithelial and Stromal Tumor of the Kidney

N. Volkan Adsay, M.D.; John N. Eble, M.D.; John R. Srigley, M.D.; Edward C. Jones, M.D.; David J. Grignon, M.D.

From Harper Hospital and Karmanos Cancer Institute, Wayne State University, Detroit, Michigan, U.S.A. (V.A., D.J.G.); VA Medical Center and Indiana University, Indianapolis, Indiana, U.S.A. (J.N.E.); The Credit Valley Hospital and McMaster University, Hamilton, Ontario, Canada (J.R.S.); and Vancouver General Hospital and University of British Columbia, Vancouver, British Columbia, Canada (E.C.J.).

Am J Surg Pathol 2000;24:958-970 Abstract quote

We describe the clinicopathologic features of 12 patients with a distinctive tumor of the kidney characterized by a mixture of epithelial and stromal elements that form solid and cystic growth patterns.

Similar tumors were reported previously in the literature under various names, including adult mesoblastic nephroma. All but one of the patients were women. The only man had a long history of treatment with lupron and diethylstilbesterol. Seven of the women had histories of long-term oral estrogen use of whom six had undergone total abdominal hysterectomy and bilateral salpingo-oophorectomy several years prior, and the seventh patient had been using oral contraceptives for many years. Another woman had this operation but did not receive any hormone therapy. Ages ranged from 31 to 71 years (mean, 56 yrs). Six patients presented with symptoms, including pain and infections attributable to mass effect, and in six the tumor was detected incidentally.

Grossly, the tumors were well-circumscribed (mean size, 6 cm; range, 312 cm) and consisted of solid and cystic components, most often in equal proportions but in variable distribution.

Microscopically, the spindle cell component ranged in appearance from scar-like fibrous tissue to leiomyoma-like interlacing fascicles; usually there was a mixture of both. More cellular foci reminiscent of ovarian stroma or solitary fibrous tumor were also present. No blastema was present. Epithelial elements (composed of clusters of tubules with variable lining) were scattered amidst the spindle cells, and focally transformed into large cysts lined by cells with abundant pink cytoplasm and a hobnail appearance. Immature epithelial elements typical of Wilms' tumor were not present. Muscle markers (desmin and smooth muscle actin) were positive diffusely and strongly in the spindle cells of all tumors, whereas HMB-45 and CD34 were absent. Estrogen receptors were detected in the nuclei of spindle cells in seven tumors and progesterone receptors in three.

The distinctive clinicopathologic characteristics of these lesions warrant their classification as a separate category of kidney tumor. We suggest the descriptive term ``mixed epithelial and stromal tumor'' for this group until its nature and relationship to other kidney lesions are further clarified. Its preponderance in females with a history of long-term estrogen replacement and the history of long-term sex-steroid use in the only male patient, combined with the frequent content of estrogen and progesterone receptors in the spindle cells, suggest that the hormonal milieu plays a role in the evolution of these tumors.

The clinical and pathologic parallels with mucinous cystic tumors of pancreas and liver raise the possibility of a common pathogenetic mechanism that may be linked to the periductal fetal mesenchyme. We think this entity is a benign composite neoplasm in which stroma and epithelium are both integral neoplastic components.

Am J Surg Pathol 2000;24:917-926.
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Last Updated 9/18/2003

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