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metanephric stromal tumor

Monday 27 October 2003

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