ESR1 and cancer: Case 6 also had bilateral breast cancer, the first tumor was left breast cancer (Stage III, IDC, ER − /PR − /HER2 +) at 28 years treated with neoadjuvant chemotherapy with anthracycline followed by a taxane plus trastuzumab regimen, and then mastectomy with Ax, with no invasive residual cancer in the breast or lymph nodes.