Abstract P3-05-08: High prevalence of splicing variant AR-V7 in triple negative breast carcinoma

Abstract

Abstract The androgen receptor (AR) and its pathway have been implicated in tumorigenesis and progression of breast cancer. Anti-androgen therapy has shown efficacy in the metastatic breast cancer and numerous clinical trials are underway to study efficacy in various clinical settings. 15 splicing variants of AR (AR-Vs) have been described in prostate cancer. Structurally, AR-Vs have insertions of cryptic exons downstream of the exons that encode the DNA-binding domain or deletions of the exons encoding the ligand-binding domain, resulting in a disrupted AR open reading frame and expression of ligand-binding-domain-truncated AR proteins. In prostate cancer, some of the AR-Vs especially AR-V7 are associated with aggressive disease and resistance to anti-AR therapy. The AR-V prevalence in human breast cancer specimens has hitherto not been studied. We aimed at studying the expression of AR-Vs in breast cancer specimens and present the data on AR-V1, AR-V7, AR8, and ARV567, in AR-positive triple negative (TNBC) and ER+/Her2- breast cancer. Design: 98 cases of TNBC, 40 cases of ER+/Her2 breast cancer and 17 cases with reduction mammoplasty were abstracted from NYULMC pathology database and screened for AR expression by immunohistochemistry (IHC). IHC for AR was performed using antibody clone N-20 (Santa Cruz) at 1:100 dilution. Normal breast tissue was used as internal control and 10% nuclear staining was used for categorizing a tumor as AR positive. A subset of cases which over-expressed AR were macrodissected from formalin fixed paraffin embedded sections with total RNA extracted by using the PureLink® FFPE RNA Isolation Kit (Invitrogen). Reverse-transcription was performed by using the SuperScript® III Reverse Transcriptase Kit (Invitrogen). AR-V expression was presented as cycle number difference to housekeeping gene (delta CT) for real-time PCR or as absolute copy number for digital PCR. Results: AR+ TNBC and AR+/ER+ cases ranged from stage 1A to IIIA. IHC for AR showed > 10% staining in 27 of 98 TNBC cases and in 39 of 40 ER+/Her2- cases. AR Positive Prevalence in TNBC and ER+ Breast Carcinoma AR+AR-TNBC2771ER+/Her2-391 AR-V7 was expressed in 11 of 13 AR+/TNBC cases (p < 0.05); AR-V1 and AR-V4 were expressed in 4; ARV8 and ARv567es were expressed in 3 and 2 cases respectively. In 25 AR+/ER+/Her2- cases AR-V7 was expressed in 14; AR-V4 in 9; ARV567 in 5, AR-V1 in 3 cases. AR Spliced Variant Incidence in TNBC, ER+ and Benign breast tissue Benign (N=17)ER+/AR+ (N=25)TNBC+/AR+(N=13)P ValueAR-V113(12%)4(25%)0.145AR-V419(36%)4(25%)0.35AR-V78(47%)14(56%)11(85%)0.021AR-V801(4%)3(19%)0.474AR-V56715(20%)2(12.5%)0.092 Conclusion: We report expression of various spliced variants in TNBC, ER+/Her2- breast cancer. A statistically significant expression of AR-V7 is seen in TNBC. Since AR-V7 predicts for poor prognosis and lack of response to anti-AR therapy in prostate cancer, AR-V7 expression maybe a useful biomarker to analyze response data in on going breast cancer clinical trials. Citation Format: Singh B, Deng F-M, Kane Y, Zhan Y, Qi Y, Liu X, Zhang H, Dong Y, Brody R, Wieczorek R, Lee P. High prevalence of splicing variant AR-V7 in triple negative breast carcinoma. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-05-08.