The current targeted hormone therapies for breast cancers that express ERα involve the inhibition or modulation of ERα transcriptional activity by selective ERα modulators (SERMs such as tamoxifen and raloxifen), aromatase inhibition (e.g., anastrozole, exemestane, and letrozole) and ERα degradation (e.g., fulvestrant). This evidence concerns the gene ESR1 and breast cancer.