Based on the addiction to estrogen signaling by ERα-positive tumors, therapies inhibiting the ERα directly, e.g., by using estrogen antagonists like tamoxifen, or indirectly, e.g., blocking estrogens using aromatase inhibitors, are the principal treatment for ER+, ER-, PR+, or HER2+ BC carriers [228]. This evidence concerns the gene ERBB2 and breast cancer.