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BCL-6 expression in mesenchymal tumours: an immunohistochemical and fluorescence in situ hybridisation study
  1. Matthew P Walters,
  2. Ellen D McPhail,
  3. Mark E Law,
  4. Andrew L Folpe
  1. Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, Minnesota, USA
  1. Correspondence to Professor Andrew L Folpe, Department of Laboratory Medicine and Pathology, Mayo Clinic, Hilton 11, Anatomic Pathology, 200 1st St SW, Rochester, MN 55905, USA; folpe.andrew{at}


The BCL-6 proto-oncogene encodes a transcriptional repressor protein. Among normal tissues, BCL-6 expression is confined to germinal center B-cells and a subpopulation of T-helper cells. Little is known about BCL-6 expression in mesenchymal tissues. We examined a series of solitary fibrous tumor (SFT) and other mesenchymal tumors for BCL-6 expression. Immunohistochemistry for BCL-6 was performed on 64 mesenchymal tumors [26 SFT (19 benign/uncertain, 7 malignant), 6 synovial sarcomas (SS), 5 gastrointestinal stromal tumors (GIST), 5 malignant peripheral nerve sheath tumors (MPNST), 5 leiomyosarcomas (LMS), 9 leiomyomas (LM) 4 desmoid tumors (DT), 4 perineuriomas (PN)]. Nuclear immunoreactivity was considered positive. Six BCL-6 positive SFT were also tested for BCL-6 gene rearrangement/amplification by FISH. Nuclear expression of BCL-6 was seen in 13/26 SFT, 5/5 LMS, 1/9 LM, 5/6 SS, 1/5 GIST, 1/5 MPNST, 1/4 PN, and 0/5 DT. BCL-6 expression was significantly more frequent in malignant (6/7) as compared with benign/uncertain SFT (6/19) (p=0.02) and in LMS (5/5) as compared with LM (1/9) (p=0.003). FISH for BCL-6 rearrangement/amplification was negative in all tested cases. We have observed BCL-6 expression in 50% or more of SFT, SS, and LMS, and in a lesser percentage of LM, GIST, MPNST and PN. Significantly more frequent expression of BCL-6 in malignant compared with benign/uncertain SFT and in LMS compared with LM suggests abnormalities in the BCL-6 signaling pathway may contribute to malignant transformation in at least some mesenchymal tumors. It is unlikely that BCL-6 expression in mesenchymal tumors is due to BCL-6 gene amplification or rearrangement. amplification or rearrangement.

  • Solitary fibrous tumour
  • bcl-6
  • immunohistochemistry
  • sarcoma
  • haematopathology
  • immunophenotyping of leukaemias/lymphomas
  • lymphoma
  • malt-lymphoma
  • cytogenetics
  • in situ hybridisation
  • molecular genetics
  • neoplasms
  • aeromonas

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  • Competing interests None declared.

  • Ethics approval Ethics approval was provided by Mayo Clinic IRB.

  • Provenance and peer review Not commissioned; externally peer reviewed.