Abstract P4-11-03: Androgen receptor expression is an independent marker of lower residual risk in the TACT2 trial (CRUK/05/019)

Introduction: TACT2 (CRUK/05/019), a multicentre randomized phase III trial in patients with node +ve or high risk node -ve invasive EBC with E-CMF as control tested two hypotheses in a 2x2 factorial design, with previously presented results showing: i) no evidence of a benefit from accelerated 2-weekly epirubicin (aE) compared to standard 3-weekly epirubicin (E) (Cameron 2012); and ii) capecitabine (X) gives equivalent efficacy but preferential side-effect profile to CMF (Canney 2014). Studies suggest that Androgen receptor (AR) expression may be associated with improved outcome in early breast cancer. We performed an analysis of AR expression in TACT2 patients to test the hypothesis that AR would represent an independent predictor of residual risk following adjuvant therapy. Methods: Tumour samples were collected prospectively from 3803/4391 TACT2 patients, Tissue micro-arrays were constructed as per published guidelines and central AR, ER, PgR, HER2, Ki67, CK5/6, EGFr and BCL2 staining performed and quantified by imaged analysis for ER, PgR, HER2, Ki67 and BCL2. EGFr and CK5/6 were dichotomised by light microscopy evaluation of cores. After planned biomarker analyses had been performed, a subset of TACT2 cases for whom remaining tissue was available were analysed for AR expression. Data for 1878 cases was available for this analysis (49% of those consenting to tissue collection). AR expression was dichotomised as AR-ve ( 10%). Log-rank tests were used to explore the prognostic value of AR on time to recurrence (TTR). Cox-regression models were used to test the independent prognostic value of AR in the presence of tumour size, grade, nodal status, and biological subtypes. Marker by treatment interaction terms were included in models to test the predictive value of AR for both randomised treatment comparisons. Results: 1398/1878 (74%) patients were classed as AR+ve and 480/1878 (26%) as AR-ve. The proportion of AR+ve patients differed significantly between biological subtypes (Luminal A 269/293 (92%); Luminal B 784/928 (84%); HER+ve 86/111 (77%); Basal-like 37/216 (17%); 5-marker-ve 37/93 (40%); χ2 p 117/480 (24%) AR-ve patients had a TTR event compared with 183/1398 (13%) AR+ve patients (HR for AR-ve compared to AR+ve =2.05 95%CI 1.63-2.59; p No differential treatment effect between AR subtypes was observed for either randomised treatment comparison (E/aE or CMF/X). Conclusion: AR is an independent prognostic marker for residual risk following chemotherapy in this large study which included patients with both luminal and non-luminal cancers. AR expression patterns differ between molecular subtypes of early breast cancer, with evidence suggesting the impact of AR on residual risk may also differ between subtypes. AR is currently being explored as another potential target for therapy so these data could have future clinical relevance. Citation Format: Jane Bayani, James Morden, Sunil Skaria, Peter Bliss, Robert Grieve, Adrian Harnett, Chris Bradley, Diana Ritchie, Peter Barrett-Lee, Peter Canney, David Cameron, Judith Bliss, John Bartlett. Androgen receptor expression is an independent marker of lower residual risk in the TACT2 trial (CRUK/05/019) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-11-03.