In the Nurses' Health Study, among the subtypes of bc, 88% of ER+, 59% of HER2+, and 32% of triple-negative breast cancers (ER–/PR–/HER2–) were positive for AR expression by immunohistochemistry. Resistance to anti-estrogen therapies could result from tumor cell adaptation from estrogen dependence to androgen dependence, according to this article.  In this case, enzalutamide could also be something for ER+ eventually. I know my onc checks my estrogen levels. I'll have to ask him about checking androgen levels.