Similarly, depletion of both ovarian progesterone and estrogens would likely be responsible for the tumor regression observed in ER-positive and ER-negative metastatic breast cancers after therapeutic oophorectomy.186 Also, the reason for tumor regression in only 20%-50% of patients with metastatic breast cancer following oophorectomy183,186,188 may be attributable to non-hormonal causes of tumor progression rather than the rest being ER-negative tumors. The gene discussed is ESR1; the disease is neoplasm.