BCOR – Antibody Lexicon

Synonyms: BCL-6 corepressor

by Jan Klos

Background

BCOR gene (at Xp11.4.) codes for the protein with the same name involved in transcriptional repression in association with BCL-6 and epigenetic silencing through polycomb repressive complex 1 (PRC1). Mutations in the BCOR gene cause a form of syndromic microphthalmia (microphthalmia, congenital cataracts, cardiac defects, dental defects and skeletal anomalies).

Staining in normal cells

identified mainly in the testis, with scattered weak positivity in the germinal centers of tonsil, but not in other human tissues.

Staining in tumors

The tumors overexpressing BCOR show most often small round blue cell morphology and myxoid background with delicate capillary channels. Clear cell sarcoma of the kidney, primitive myxoid mesenchymal tumor of infancy and high-grade neuroepithelial tumor with BCOR alteration in central nervous system all share similar internal tandem duplications in the polycomb-group. Translocations resulting in BCOR fusion with CCNB3, MAML3 and ZC3H7B have been identified in undifferentiated round cell sarcoma. Subsets of high-grade endometrial stromal sarcoma and ossifying fibromyxoid tumor which have a more aggressive clinical course have been shown to harbor ZC3H7B-BCOR fusions. Expression of SATB2 is seen in majority of BCOR+ cases which show usually rearrangements of YWHAE-NUTM2B, BCOR-MAML3, BCOR ITD (75%), BCOR-CCNB3 (71%), and a in about 1/3 of CCSKs. Loss-of-function mutations are reported in a subset of myelodysplasia, AML (Acute Myeloid Leukemia) and in some subtypes of lymphoma (eg. extranodal NK/T-cells lymphoma, nasal type, splenic diffuse red pulp lymphoma, prolymphocytic T-cell leukemia and chronic lymphocytic leukemia). BCOR mutations are found also in aggressive B3-thymomas, adenoid cystic carcinoma, uterine corpus endometrial carcinoma, EBV + gastric carcinomas, colon and stomach adenocarcinoma, and lung tumors, regardless of histology.

Staining pattern

Staining pattern is nuclear.

Control tissue

Control tissue testis (all spermatogonia should show nuclear positivity while other cells are negative).

Application

BCOR is a highly sensitive and specific marker and it can be used as a diagnostic marker to identify molecular subsets of the following tumors:

Small Blue Round Cell Tumors (SBRCTs)
Clear Cell Sarcoma of Kidney (CCSK)
Primitive myxoid mesenchymal tumor of infancy
High-grade neuroepithelial tumors in CNS
Undifferentiated round cell sarcoma
Subsets of high-grade endometrial stromal sarcoma and ossifying fibromyxoid tumor
About 50% of synovial sarcomas with BCOR abnormalities and YWHAE-rearrangements
SATB2, Cyclin D1, TLE1 and Bcl2 immunoreactivity is also present in around 80% of these tumors.
Positive staining does not differentiate between tumors with rearranged of BCOR gene and tumors with overexpression of protein without rearrangement of gene

by Jan Klos

Background

Staining in normal cells

Staining in tumors

Staining pattern

Control tissue

Application

Selected references