metanephric stromal tumor

Definition: Metanephric stromal tumors are rare renal stromal tumors that predominantly affect children. They belong to the metanephric family of tumors along with metanephric adenofibroma and metanephric adenoma .

Epidemiology

 Mean patient age : 2 years

Macroscopy

 fibrous lesion centered in the renal medulla containing smooth-walled cysts (mean tumor size, 5.5 cm)

Microscopically

 histologically identical to the stromal component of metanephric adenofibroma (MAF, previously termed nephrogenic adenofibroma)
 unencapsulated spindle cell lesion that entraps native kidney
 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)
 vascular alterations

Immunochemistry

 CD34+/-

Prognosis

 surgical excision alone
 none recurrence or metastasis known

Differential diagnosis

 clear cell sarcoma of the kidney

Molecular pathology

 BRAF exon 15 mutation

• found in 11/17 cases (65%) of metanephric stromal tumors, all corresponding to a thymidine to adenine substitution at codon 600 (BRAF V600E).
• All other renal stromal tumors tested were negative for BRAF exon 15 mutations. -* BRAF V600E mutations are encountered in the majority of metanephric stromal tumors, supporting a link with other metanephric tumors and suggesting a clonal event possibly affecting primordial renal cells.
• BRAF V600E mutations have been associated with oncogene-induced senescence in other benign tumors, providing clues to the pathogenesis of these neoplasms in keeping with their overall benign behavior.
• Results also suggest a potential diagnostic use for BRAF exon 15 mutations in differentiating metanephric stromal tumors from other pediatric renal stromal tumors, particularly in limited samples.
• BRAF exon 15 mutations have been observed in 88% of metanephric adenomas and in isolated cases of metanephric adenofibroma.

Open access references

 Metanephric stromal tumor: a novel pediatric renal neoplasm. Rajalakshmi V, Chandran P; Selvambigai, Ganesh J. Indian J Pathol Microbiol. 2009 Jul-Sep;52(3):389-91. PMID: 19679970 (Free)

References

 Metanephric Stromal Tumor Arising in a Patient With the Neurofibromatosis Type 1 Syndrome. McDonald OG, Rodriguez R, Bergner A, Argani P. Int J Surg Pathol. 2009 Oct 28. PMID: 19875383

 Metanephric stromal tumor with urothelial extension. Lorenzo AJ, Timmons C, Weinberg A, Megison SM, Snodgrass WT. J Urol. 2003 Mar;169(3):1095-7. No abstract available. PMID: 12576860

 Adult presentation of metanephric stromal tumor. Bluebond-Langner R, Pinto PA, Argani P, Chan TY, Halushka M, Jarrett TW. J Urol. 2002 Oct;168(4 Pt 1):1482-3. PMID: 12352423

 Metanephric stromal tumor: a rare benign pediatric renal mass. Palese MA, Ferrer F, Perlman E, Gearhart JP. Urology. 2001 Sep;58(3):462. PMID: 11549506

 Argani P, Beckwith JB. Metanephric stromal tumor: report of 31 cases of a distinctive pediatric renal neoplasm. Am J Surg Pathol. 2000 Jul;24(7):917-26. PMID: 10895814