Androgen receptor in breast cancer: A wolf in sheep's clothing? A lesson from prostate cancer

The possibility that a receptor for androgen is expressed in Breast Cancer (BC) is fascinating given that the tumor is predominantly estrogen-dependent. The androgen receptor (AR) is emerging as a new marker and a potential new therapeutic target in the treatment of BC patients. The recent availability of selective AR inhibitors (e.g. bicalutamide, enzalutamide, apalutamide) approved for the treatment of prostate cancer has opened up the possibility to use them in BC patients whose tumors express AR. However, AR appears to have various functions according to the BC subtype, e.g. ER-positive or triple negative BC and the patient prognosis is different on the basis of the presence or absence of estrogen and progesterone receptors. Moreover, a different AR expression was seen according to the various ethnicities. Of note, in population at low economical income, the availability of anti-AR compounds at low cost could open the possibility to treat AR-positive triple negative BC that are highly present in these populations. Up to now, AR detection is not routinely performed in BC. The standardization of AR detection methods could render AR an easily detectable marker in primary BC and metastatic samples. Nevertheless, the overall concordance of 60% of AR expression in primary tumor and metastasis implies that a clinician who need the AR value to give anti-AR therapy should have the data on both the tumor materials. Following the comprehensive studies on prostate cancer the possibility to test AR on liquid biopsies suggest the use of this biomarker for a real-time disease monitoring. Finally, considering the possibility to treat patients with immune checkpoint inhibitors there is the need to know the relation between microenvironment and AR in BC.