Abstract 496: Androgen receptor expression on circulating tumor cells in metastatic breast cancer

Background: Androgen receptor (AR) is a nuclear transcription factor and a member of the steroid hormone receptor superfamily that can be detected by immunohistochemical staining in all three subtypes of invasive breast cancer with frequency of >70% of estrogen receptor-positive tumors (ER+), >60% of HER2-positive tumors (HER2+), and 40-50% of triple-negative breast cancers (TNBC) respectively. AR-target therapies are showing early activity in AR+ breast cancer. Given early evidence of activity with agents targeting AR, it is desirable to improve our understanding of the AR biology in breast cancer. Although circulating tumor cells (CTCs) have been proposed as a liquid biopsy for biomarker detection in multiple cancer types, the rate and heterogeneity of AR expression in CTCs in breast cancer is still unclear. In this study, we determine the rate and heterogeneity of AR expression in CTCs of patients with metastatic breast cancer. Methods: Blood samples from patients with metastatic breast cancer were smeared onto glass slides and subjected to nuclear staining with DAPI and reacted with fluorescent-labeled antibodies to detect CD45 on leukocytes and cytokeratin and AR on epithelial cells; the slides were scanned on the Epic Sciences CTC platform and the data analyzed using established algorithms. Results: Among the 59 patients analyzed, 25 (42.4%) had ER+/HER2-, 12 (20.3%) had ER+/HER2+, 6 (10.2%) had ER-/HER2+, and 16 (27.1%) had TNBC based on the most recent staining. CTCs were detected in 50 of 59 (84.7%) patients. Characterization of CTCs identified CK+ CTCs (45 of 59, 76.3%), CK-negative CTCs (16 of 59, 27.1%), CK+ CTC clusters (16 of 59, 27.1%), and apoptotic CTCs (45 of 59, 76.3%), respectively. Number of CTCs per patient ranged from 0 to 282.1 per mL (median = 4.4). Six of the 50 patients (12%) with CTCs had AR+ CTCs. The number of AR+ CTCs per patient ranged from 0.3 to 52.6 per mL (median = 1.15). Among the patients with AR+ CTCs, the percentage of CTCs that were AR+ ranged from 5% to 50% (median = 21%). Among the six patients with AR+ CTCs, five patients had ER+ breast cancer and one had TNBC. Conclusions: We demonstrated that the Epic Sciences non-enriching or selecting platform can detect AR expression in CTCs in breast cancer. These preliminary results suggest the need for clinical validation of CTC AR expression as a potential test to stratify and identify patients who might benefit from AR therapy. The heterogeneity of intra-patient CTC AR expression leads us to another hypothesis that patients with AR+ CTCs might have heterogeneous disease with multiple drivers. Further studies are warranted to allow serial monitoring of changes in AR and to investigate the clinical applicability of AR+ CTCs and their heterogeneity. Citation Format: Takeo Fujii, Yipeng Wang, James M. Reuben, Rachel Krupa, Ryon Graf, Lyndsey Dugan, Jessica Kouw, Dena Marrinucci, Bora Lim, Carlos H. Barcenas, Angela N. Marx, Debu Tripathy, Ryan Dittamore, Naoto T. Ueno. Androgen receptor expression on circulating tumor cells in metastatic breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 496.