In accordance with previous studies, Western blot analysis of endogenous Foxo3a in established mammary epithelial cell lines indicated that the level of Foxo3a in the ER-positive breast cancer cell line (MCF-7) was significantly higher than the two ER-negative cell lines (MDA-MB-231 and MDA-MB-435), as shown in Figure 4A, B. This evidence concerns the gene FOXO3 and breast cancer.