In agreement with the finding that transgenic mice overexpressing AIB1 (Amplified In Breast Cancer 1) developed mammary epithelial cell proliferation, hyperplasia and tumorigenesis, low levels of miR-17-5p in breast cancer correlated with increased expression of the mRNA encoding AIB1, and conversely, miR-17-5p overexpression suppressed cell proliferation [24–26]. This evidence concerns the gene NCOA3 and breast cancer.