Because BZA is already clinically approved for use in hormone replacement therapy and is a potent ERα antagonist in the breast, an agonist in bone, and neutral in the endometrium with long-term safety data in thousands of patients, we explored its ability to inhibit the Y537S and D538G ERα somatic mutants in breast cancer (Wardell et al., 2013a). The gene discussed is ESR1; the disease is breast carcinoma.