This strategy was tested in three breast cell lines, controlling for oxygen availability and pHe levels in the microenvironment: (i) MCF10A normal breast epithelial cells; (ii) naïve and acid-adapted (AA) MCF7 estrogen receptor-positive (ER+) breast cancer cells; and (iii) naïve and AA triple-negative MDA-MB-231 breast cancer cells. Here, ESR1 is linked to breast cancer.