Kidney tumor
Childhood tumors
Metanephric adenofibroma

Editorial Board Member: Maria Tretiakova, M.D., Ph.D.
Editor-in-Chief: Debra L. Zynger, M.D.

Topic Completed: 23 November 2020

Minor changes: 23 November 2020

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PubMed Search: Metanephric adenofibroma kidney

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Cite this page: Chami R. Metanephric adenofibroma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumormetaadenofibroma.html. Accessed November 23rd, 2020.
Definition / general
  • Biphasic neoplasm composed of epithelial and stromal components
  • Member of metanephric tumor family including metanephric adenoma (purely epithelial) and metanephric stromal tumor (purely stromal)
Essential features
  • Biphasic neoplasm composed of varying proportions of stromal and epithelial components
  • Typically solitary and nonencapsulated
  • No nuclear atypia in both components
  • Mitotic figures are absent or rare in epithelial component
  • Epithelial component is identical to metanephric adenoma
  • Stromal / mesenchymal component is identical to metanephric stromal tumor
Terminology
  • Previously known as nephrogenic adenofibroma
ICD coding
Epidemiology
Sites
  • Metanephric adenofibroma occurs in renal cortex and medulla
Pathophysiology
  • Unknown, however, several cases have been reported to harbor BRAF V600E mutations; genomic alterations in BRAF oncogene appear at an early stage in tumorigenesis and are preserved through the tumor progression and therefore are considered as drivers of oncogenesis (Hum Pathol 2015;46:1153, Am J Surg Pathol 2015;39:1301)
Etiology
  • Uncommon renal neoplasm; unknown etiology
Clinical features
Diagnosis
  • The diagnosis is made by microscopic examination of resected tissue
Radiology description
Radiology images

Images hosted on other servers:

Homogenous solid mass, no calcification or necrosis

Prognostic factors
  • Benign
  • One case of metanephric adenofibroma in combination with Wilms tumor and renal papillary carcinoma has been reported in literature (Pediatr Dev Pathol 2012;15:65)
Case reports
Treatment
  • Excision of the tumor is adequate therapy
Gross description
  • Solitary, unencapsulated, vaguely circumscribed / indistinct borders
  • Tan / gray / white-yellow cut surface
  • Partially cystic
  • Reference: Am J Surg Pathol 2001;25:433
Gross images

Images hosted on other servers:

Largely solid, tan homogenous renal mass

Fibrous, white grey cut surface

White solid and cystic cut surface

Microscopic (histologic) description
  • Biphasic tumor composed of varying proportions of stromal and epithelial components
  • Epithelial component identical to metanephric adenoma, tightly packed small tubules, papillary structures or glomeruloid structures (blunt short papillae resembling glomeruli)
  • Epithelial cells have small round to oval nuclei with delicate chromatin and absent or inconspicuous nucleoli and slight pale cytoplasm; mitotic figures are absent or rare
  • Psammoma bodies are common
  • Mesenchymal component identical to metanephric stromal tumor, bland spindle and epithelioid / plump cells with thin hyperchromatic nuclei and indistinct cell borders
  • Areas of intratumoral angiodysplasia, concentric cuffing of entrapped tubules ("onion skinning") and heterologous differentiation (cartilage, adipose tissue or glia) (Am J Surg Pathol 2001;25:433)
  • No vascular invasion
Microscopic (histologic) images

Contributed by Rose Chami, M.D.
Biphasic tumor with epithelial and stromal components Biphasic tumor with epithelial and stromal components

Biphasic tumor with epithelial and stromal components

Highly cellular tumor

Highly cellular tumor

Tubular and glomeruloid structures

Tubular and glomeruloid structures

Psammoma bodies

Psammoma bodies


Cellular solid appearance

Cellular solid appearance

Spindle cell component

Spindle cell component

AE1/AE3

AE1/AE3

WT1, both components

WT1, both components

WT1, epithelial component

WT1, epithelial component


WT1, stromal component

WT1, stromal component

CD34, both components

CD34, both components

BRAF V600E, epithelial component

BRAF V600E, epithelial component

Positive stains
Negative stains
Molecular / cytogenetics description
Sample pathology report
  • Right kidney, partial nephrectomy:
    • Metanephric adenofibroma, 3.2 cm, resection margins negative for tumor (see comment)
    • Comment: There is a nonencapsulated biphasic renal tumor composed of epithelial and stromal components. There is no nuclear atypia in both components and mitotic figures are rare or absent in the epithelial component. Immunopositive for BRAF V600E.
Differential diagnosis
Board review style question #1

    A pediatric renal tumor is shown. Which of the following is true about this entity?

  1. Biphasic neoplasm with varying proportions of stromal and epithelial components
  2. Epithelial component is mitotically active
  3. Malignant and frequently metastasizing
  4. Multifocal (typically)
Board review answer #1
A. This is metanephric adenofibroma. It is a biphasic neoplasm with varying proportions of stromal and epithelial components.

Reference: Metanephric adenofibroma

Comment Here
Board review style question #2
    Which of the following is true about the expression of metanephric adenofibroma?

  1. CD57-
  2. CK7+
  3. Desmin+
  4. WT1+
Board review answer #2
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