FLI-1 distinguishes ewing sarcoma from small cell osteosarcoma and mesenchymal chondrosarcoma

Anna F. Lee, Malcolm M. Hayes, David Lebrun, Inigo Espinosa, G. Petur Nielsen, Andrew E. Rosenberg, Cheng Han Lee

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


Small cell osteosarcoma and mesenchymal chondrosarcoma are 2 primary bone tumors with a small round blue cell component, which can mimic the appearance of Ewing sarcoma. Distinguishing these tumors from each other on biopsy material is important clinically, as optimal therapy differs according to the tumor type. However, separating these entities on morphology alone can be challenging. FLI-1 has been described to be a useful marker for Ewing sarcoma, particularly when hematolymphoid markers are negative. In small cell osteosarcoma and mesenchymal chondrosarcoma, the FLI-1 staining pattern has not been adequately characterized. Using a monoclonal FLI-1 antibody, nuclear immunoreactivity in tumor cells was evaluated in 10 small cell osteosarcomas, 10 mesenchymal chondrosarcomas, and 8 Ewing sarcomas, together with a number of other small, round, blue cell tumors. None of the small cell osteosarcomas or mesenchymal chondrosarcomas exhibited FLI-1 staining in the tumor cells, in contrast to the positive nuclear FLI-1 staining in the stromal endothelial cells. In comparison, 6 of the 8 Ewing sarcomas showed moderate-to-strong nuclear FLI-1 staining of the tumor cells in addition to strong staining of the stromal endothelial cell nuclei. With the exception of lymphoblastic lymphomas, FLI-1 positivity was not seen in the other small round blue cell tumors examined. These findings show that, in contrast to Ewing sarcoma, small cell osteosarcoma and mesenchymal chondrosarcoma lack FLI-1 immunoreactivity. FLI-1 is therefore useful in the differential diagnosis of small round blue cell tumors of the bone.

Original languageEnglish (US)
Pages (from-to)233-238
Number of pages6
JournalApplied Immunohistochemistry and Molecular Morphology
Issue number3
StatePublished - May 2011
Externally publishedYes


  • ewing sarcoma
  • FLI-1
  • immunohistochemistry
  • mesenchymal chondrosarcoma
  • small cell osteosarcoma
  • small round blue cell tumor

ASJC Scopus subject areas

  • Pathology and Forensic Medicine
  • Medical Laboratory Technology
  • Histology


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