Stains & molecular markers

Topic Completed: 21 July 2020

Minor changes: 8 February 2021

Copyright: 2020,, Inc.

PubMed Search: BCOR[TI] free full text[SB]

Isidro Machado, M.D., Ph.D.
Antonio Llombart-Bosch, M.D., Ph.D.
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Cite this page: Machado I, Llombart-Bosch A. BCOR. website. Accessed April 16th, 2021.
Definition / general
Essential features
  • BCOR immunohistochemistry can be used diagnostically to separate tumors with BCOR gene alteration (rearrangement or internal tandem duplication) from their histological mimics (mainly the group of small / ovoid round cell sarcomas) (Pediatr Blood Cancer 2014;61:2191, Histopathology 2020;76:509)
  • BCOR is a corepressor when bound to BCL6 (Genes Dev 2000;14:1810)
  • BCOR forms part of the polycomb repressive complex 1 which ubiquitinates H2AK119 causing epigenetic silencing (Biochem Soc Trans 2017;45:193)
  • Involved in early embryonic development and the differentiation of embryonic stem cells into ectoderm, mesoderm and hematopoietic lineages (PLoS One 2008;3:e2814)
  • BCOR-CCNB3 fusion results from an X chromosomal paracentric inversion linking the BCOR sequence to exon 5 of CCNB3 (Histopathology 2018;72:320)
Clinical features
Uses by pathologists
Microscopic (histologic) images

Contributed by Isidro Machado, M.D., Ph.D.
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Undifferentiated round cell sarcoma

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Undifferentiated round cell sarcoma, BCOR positive

Positive staining - normal
Positive staining - disease
Negative staining
Board review style question #1
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    A soft tissue tumor is shown with corresponding BCOR IHC. Which of the following is the most likely diagnosis?

  1. BCOR rearranged sarcoma
  2. CIC rearranged sarcoma
  3. Desmoplastic small round cell tumor
  4. Ewing sarcoma
Board review style answer #1
A. BCOR rearranged sarcoma

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Reference: BCOR
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