Kidney tumor

Benign adult tumors

Solitary fibrous tumor



Topic Completed: 24 September 2021

Minor changes: 24 September 2021

Copyright: 2003-2021, PathologyOutlines.com, Inc.

PubMed Search: Solitary fibrous tumor [TI] free full text[sb] kidney

Lin Cheng, M.D., Ph.D.
Maria Tretiakova, M.D., Ph.D.
Page views in 2020: 1,151
Page views in 2021 to date: 1,913
Cite this page: Cheng L, Tretiakova M. Solitary fibrous tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/kidneytumorsolitary.html. Accessed December 6th, 2021.
Definition / general
  • Fibroblastic mesenchymal tumor with haphazard spindle cells, staghorn vasculature and NAB2-STAT6 gene fusion
Essential features
  • Fibroblastic tumor with patternless pattern and staghorn vasculature
  • STAT6 expression by immunohistochemistry; NAB2-STAT6 gene fusion
  • About 16% of renal solitary fibrous tumors (SFTs) show histological features that may indicate aggressive behavior (histologically malignant): hypercellularity, cytological atypia, increased mitosis and necrosis
  • Histologically malignant does not equal clinically malignant
Terminology
  • Hemangiopericytoma (not recommended)
ICD coding
  • ICD-O: 8815/0 - solitary fibrous tumor
  • ICD-10: D49.519 - neoplasm of unspecified behavior of unspecified kidney
  • ICD-11: XH7E62 - solitary fibrous tumor, NOS
Epidemiology
Sites
Pathophysiology
  • Intrachromosomal inversion of chromosome 12q results in NAB2-STAT6 fusion (Nat Genet 2013;45:131)
  • NAB2 is a transcriptional repressor of early growth response 1 (EGR1), while NAB2-STAT6 is a transcriptional activator of ERG1 (Nat Genet 2013;45:180)
  • Overactivation of EGR1 leads to increased expression of its target genes, such as IGF2, FGF2, PDGFD, FGFR1, NTRK1, etc. (Nat Genet 2013;45:180)
Diagrams / tables

Images hosted on other servers:

4 variable risk stratification

Clinical features
Diagnosis
  • Histological examination
  • NAB2-STAT6 gene fusion by immunohistochemical or molecular studies
Radiology description
Radiology images

Images hosted on other servers:

Ultrasound, heterogeneous hyperechoic mass

CT, Heterogeneous enhancing mass

MRI, heterogeneous mass

Prognostic factors
  • Histological features cannot precisely predict aggressive behavior; only 36% of histologically malignant kidney SFT patients presented with recurrent / metastatic disease (Int J Surg Pathol 2015;23:34)
  • Adverse prognostic factors in SFTs of all anatomic sites: age ≥ 55, tumor size ≥ 10 cm, mitotic count ≥ 4/10 high power fields, tumor necrosis ≥ 10% (Mod Pathol 2017;30:1433)
Case reports
Treatment
  • Complete surgical resection
  • Ablation or systemic chemotherapy for unresectable tumors
Clinical images

Images hosted on other servers:

Tumor deforming right kidney

Gross description
  • Average tumor size of benign kidney SFTs: 8 cm (Int J Surg Pathol 2016;24:281)
  • Firm, rubbery, usually well circumscribed
  • White-tan or yellow-tan cut surface
  • Myxoid changes, hemorrhage and necrosis can be seen
Gross images

Images hosted on other servers:

Yellow-tan mass

Rubbery white-tan mass

Adipose tissue and hemorrhage

Frozen section description
  • Spindle cell neoplasm with patternless pattern and staghorn vessels
Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Maria Tretiakova, M.D., Ph.D.
Patternless pattern

Patternless pattern

Staghorn vessels

Staghorn vessels

Necrosis

Necrosis

Entrapped tubules

Entrapped tubules

STAT6

STAT6

CD34

CD34

Cytology description
  • Histologically benign: low to moderate cellularity of clusters and single cells, spindle, oval or stellate cells with monotonous nuclei, wispy cytoplasm, collagenous intercellular stroma (Cancer Cytopathol 2018;126:36)
  • Histologically malignant: hypercellular, crowded clusters, focal nuclear pleomorphism, mitoses, necrosis (Cancer Cytopathol 2010;118:83)
Cytology images

Images hosted on other servers:

Benign SFT

Malignant SFT

Positive stains
Electron microscopy description
  • Cells with fibroblastic features, well developed rough endoplasmic reticulum, surrounded with collagen fibers (Med Mol Morphol 2009;42:239)
Molecular / cytogenetics description
Molecular / cytogenetics images

Images hosted on other servers:

Structure of NAB2-STAT6

NAB2-STAT6 gene fusion

Sample pathology report
  • Left kidney, nephrectomy:
    • Solitary fibrous tumor, 3.5 cm, margins of resection free of involvement (see comment)
    • Comment: Clinically, this patient presented with hematuria and flank pain. CT showed a left renal mass. No other lesions or history of any malignancies are identified. The histological sections of the renal mass show both hypo and hypercellular areas composing of monotonous spindle cells in haphazard pattern with staghorn vascular network. No mitosis or necrosis is seen. Immunohistochemistry studies show that the spindle cells are positive for STAT6, CD34, BCL2 and vimentin and negative for PAX8, CK8/18, MDM2 and S100. The overall findings favor a solitary fibrous tumor, likely renal primary. According to the modified risk stratification criteria, this tumor is classified as low risk. Clinical correlation is recommended (Mod Pathol 2017;30:1433).
Differential diagnosis
Board review style question #1

Which of the following are the most commonly seen histological features of solitary fibrous tumor of kidney?

  1. Admixture of adipose tissue, smooth muscle and thick wall vessels
  2. Haphazard arrangement of spindle cells and staghorn vasculatures
  3. Spindle cells with cytoplasmic microvacuoles and complex capillary network
  4. Storiform fibrosis
  5. Sustentacular cells wrap around chief cells and form zellballen pattern
Board review style answer #1
B. Haphazard arrangement of spindle cells and staghorn vasculatures

Comment Here

Reference: Solitary fibrous tumor
Board review style question #2
Which immunostain is usually negative in solitary fibrous tumor of kidney?

  1. BCL2
  2. CD34
  3. CD99
  4. MDM2
  5. STAT6
Board review style answer #2
Back to top
Image 01 Image 02