ESR1 and breast cancer: Accordingly, two insights could explain the contradictory effects of AR positivity on ER+ BCs: (i) the AR appears to have context-dependent roles as it shifts from an anti-proliferative stimulus to a pro-proliferative one, depending on the high and low expression levels of ER, respectively, and (ii) although AR positivity likely reflects well-differentiated BCs and is thus associated with a good prognosis, the biological effects of AR signaling, when over-stimulated by genomic or non-genomic mechanisms, may confers worse outcomes in BC, which has been recently suggested [141].