Studies performed by others [17], [18], together with unpublished experiments performed in our laboratory in breast cancer BT549 cells and MDA-MB-231 cells (mentioned in Section B.1) have shown that the yield of cell transfectants expressing appreciable levels of ectopically mono-cistronic transduced ERα is very low (5–12.5%). The gene discussed is ERAL1; the disease is breast carcinoma.