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BQ323636.1, a novel splice variant to NCOR2, as a predictor for tamoxifen resistant breast cancer

Gong, Chun; Man, Ellen P.S.; Tsoi, Ho; Lee, Terence K.W.; Paul, Lee; Mak, Sai-Ting; Wong, Lai-Shan; Luk, Mei-Yee; Rakha, Emad A.; Green, Andrew R.; Ellis, Ian O.; Lam, Eric W.F.; Cheung, Kwok-Leung; Khoo, Ui-Soon

BQ323636.1, a novel splice variant to NCOR2, as a predictor for tamoxifen resistant breast cancer Thumbnail


Chun Gong

Ellen P.S. Man

Ho Tsoi

Terence K.W. Lee

Lee Paul

Sai-Ting Mak

Lai-Shan Wong

Mei-Yee Luk

Professor of Breast Cancer Pathology

Eric W.F. Lam

Ui-Soon Khoo


Purpose: Adjuvant tamoxifen treatment revolutionized the management of estrogen receptor (ER) positive breast cancers to prevent cancer recurrence; however drug resistance compromises its clinical efficacy. The mechanisms underlying tamoxifen resistance are not fully understood and no robust biomarker is available to reliably predict those who will be resistant. Here we study BQ323636.1, a novel splice variant of the NCOR2 gene and evaluate its efficacy in predicting tamoxifen resistance in breast cancer patients.
Experimental Design: A monoclonal anti-BQ323636.1 antibody that specifically recognizes the unique epitope of this splice variant was generated for in vitro mechanistic studies and for in vivo analysis by immunohistochemistry on tissue microarrays of two independent cohorts of 358 patients with more than 10 years clinical follow-up data, who had ER-positive primary breast cancer and received adjuvant tamoxifen treatment. Orthotopic mouse model was also used.
Results: Overexpression of BQ323636.1 conferred resistance to tamoxifen in both in vitro and in orthotopic mouse model. Mechanistically, co-immunoprecipitation showed BQ could bind to NCOR2 and inhibit the formation of co-repressor complex for the suppression of ER signaling. Nuclear BQ overexpression in patients samples was significantly associated with tamoxifen resistance (p= 1.79 x 10-6, sensitivity 52.9%, specificity 72.0%). In tamoxifen-treated patients, nuclear BQ overexpression was significantly correlated with cancer metastasis and disease relapse. Nuclear BQ was also significantly associated with poorer overall survival (p=1.13 x 10-4) and disease-specific survival (p=4.02 x 10-5).
Conclusions: These findings demonstrate that BQ can be a reliable biomarker to predict tamoxifen resistance in ER-positive breast cancer patients.

Journal Article Type Article
Acceptance Date Jan 23, 2018
Online Publication Date Feb 2, 2018
Publication Date Aug 28, 2018
Deposit Date Jan 4, 2018
Publicly Available Date Feb 3, 2019
Journal Clinical Cancer Research
Print ISSN 1078-0432
Electronic ISSN 1557-3265
Publisher American Association for Cancer Research
Peer Reviewed Peer Reviewed
Volume 24
Issue 15
Pages 3681-3691
Keywords NCOR2/SMRT; BQ323636.1; Tamoxifen-resistance; breast cancer
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