Stains & CD markers

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Last staff update: 19 May 2022

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PubMed Search: FLI1 [title] stain

Muhammad Raza, M.B.B.S.
Nasir Ud Din, M.B.B.S.
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Cite this page: Raza M, Ud Din N. FLI1. website. Accessed February 23rd, 2024.
Definition / general
  • FLI1 (Friend leukemia integration 1) gene is a proto-oncogene located on chromosome 11q24
Essential features
  • Due to the increasing number of tumors found to express FLI1, more specific markers or molecular confirmation is necessary for the diagnosis of Ewing sarcoma
  • Key member of the ETS family of transcription factors and closely related to ERG (Am J Respir Cell Mol Biol 2017;57:121)
  • Crucial role in maintenance and differentiation of hematopoietic stem cells and angiogenesis
Uses by pathologists
  • To differentiate Ewing sarcoma from other round blue cell tumors
    • 90% of Ewing sarcoma have EWS-FLI1 fusion
    • Distinguish Ewing sarcoma of kidney (positive) from blastema predominant Wilms tumor (negative)
    • Distinguish Ewing sarcoma (positive) from small cell osteosarcoma or mesenchymal chondrosarcoma (negative) (Appl Immunohistochem Mol Morphol 2011;19:233)
  • Diagnosis of benign and malignant vascular tumors (positive) (Am J Surg Pathol 2001;25:1061)
Prognostic factors
Microscopic (histologic) images

Contributed by Nasir Ud Din, M.B.B.S.
Ewing sarcoma, H&E Ewing sarcoma, H&E

Ewing sarcoma, H&E

Pseudomyogenic hemangioendothelioma, H&E

Pseudomyogenic hemangio-endothelioma, H&E

Angiosarcoma, H&E

Angiosarcoma, H&E

Ewing sarcoma, FLI1 Ewing sarcoma, FLI1

Ewing sarcoma, FLI1

Pseudomyogenic hemangioendothelioma, FLI 1

Pseudomyogenic hemangio-endothelioma, FLI 1

Angiosarcoma, FLI1

Angiosarcoma, FLI1

Positive staining - normal
  • Endothelial cells, T and B lymphocytes
Positive staining - disease
Negative staining
Sample pathology report
  • Liver, left lobe mass, trucut biopsy:
    • Features are consistent with epithelioid hemangioendothelioma (see comment)
    • Comment: Histological examination shows cores of a neoplasm composed of cords, clusters and small nests of round to polygonal cells. These cells have vesicular nuclei, conspicuous nucleoli and eosinophilic cytoplasm. Intracytoplasmic lumina are noted, occasionally containing red blood cells. The background is hyalinized with myxoid areas. Tumor cell are diffusely positive for CD31, CD34, ERG and FLI1 and focally positive for CK CAM5.2.
Board review style question #1

Discolored skin from left foot of a 70 year old Caucasian man was biopsied and shows compressed, slit-like vascular channels infiltrating dermis admixed with proliferation of moderately atypical, spindled cells. Which is the best immunohistochemical profile that confirms the diagnosis of Kaposi sarcoma?

  1. CD31 positive, CD34 positive, ERG positive
  2. ERG negative, HHV8 positive, EMA positive
  3. ERG positive, CD34 positive, FLI1 negative
  4. FLI1 positive, HHV8 positive, CD31 positive
  5. LMP1 positive, MOC31 negative, p63 positive
Board review style answer #1
D. FLI1 positive, HHV8 positive, CD31 positive. FLI1 is a highly sensitive vascular marker, while CD31 is both sensitive and specific, thus confirming the vascular origin. HHV8 positivity is seen in Kaposi sarcoma among vascular tumors.

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Reference: FLI1
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