Abstract P5-02-08: Androgen receptor pathway activity and the ratio between androgen and estrogen receptor pathway activity in breast cancer subtypes
Authors: van de Stolpe Anja , Wesseling-Rozendaal Yvonne , de Inda Marcia Alves , van Ooijen Henk , Verhaegh Wim 
Published: March 2020

Abstract
Background: Androgen receptor (AR) immunohistochemistry staining in breast cancer has revealed frequent AR expression in all breast cancer subtypes. Activity of the AR signaling pathway can be either tumor suppressive or tumor promoting, depending on tumor context (Pharmacol Ther., In press, https://doi.org/10.1016/j.pharmthera.2019.05.005). For this reason, in an individual patient, AR phenotypic activity needs to be defined in order to choose the proper AR targeted therapy. The AR/ER protein ratio has been suggested as a biomarker to define this AR function and enable the appropriate therapy choice, i.e. androgen therapy in case of a low AR/ER protein expression ratio, and anti-androgen therapy in case of a high ratio. However, AR and ER expression are not necessarily associated with an active signaling pathway. Therefore we investigated the ratio between functional AR and ER pathway activities as this may have an advantage in guiding therapy choice. Methods: AR and ER pathway activity and AR/ER pathway activity ratio were determined on public Affymetrix HG-U133 Plus 2.0 gene expression microarray data of clinical breast cancer studies (available in the GEO database: GSE12276, GSE21653, GSE20685, GSE42568, GSE6532, GSE9195, GSE45827, GSE7307, GSE10780, GSE17907, GSE21422, GSE5764, GSE31192, GSE54002 and Array Express: E-MTAB-365; total n=2090). For this, we used previously described tests that enable quantification of functional pathway activity, based on Bayesian computational model inference of pathway activity from measurements of mRNA levels of target genes of the ER and AR transcription factor (Cancer Res., 2014, vol. 74, no. 11, pp. 2936-2945; Sci Rep., 2019, vol. 9, no. 1, p. 1603). Intrinsic subtyping of all samples has been done using the same methodology as described elsewhere (Am J Pathol, 2018, vol. 188, no. 9, pp 1956-1972).Results: AR pathway activity was increased in all breast cancer subtypes compared to normal breast tissue (p&lt;0.0001); highest AR activity scores were observed in the HER2-enriched subtype. As shown before, ER activity scores were highest in luminal A and B subtypes. The AR/ER pathway activity ratio was low in luminal A and B, and comparable with normal tissue, but high in HER2 and basal breast cancer subtypes (p&lt;0.0001). Discussion: Results are compatible with currently available evidence and show that the AR pathway can be activated in all breast cancer subtypes. We hypothesize that its function depends on the level of co-existent ER pathway activity, i.e. a tumor suppressive function in ER pathway active breast cancer, and a tumor promoting function in ER pathway inactive breast cancer. Upon future clinical conformation, the AR/ER pathway activity ratio as determined on an individual patient tissue sample may be an improved biomarker to guide the choice of (complementary) AR pathway targeted therapy in breast cancer, i.e. androgen receptor pathway inhibitors in case of a high ratio and potential use of androgen receptor modulators in case of a low ratio.
Citation Format: Anja van de Stolpe, Yvonne Wesseling-Rozendaal, Marcia Alves de Inda, Henk van Ooijen, Wim Verhaegh. Androgen receptor pathway activity and the ratio between androgen and estrogen receptor pathway activity in breast cancer subtypes [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-02-08.