Very early studies found that when evaluating 13 breast cancer cell lines, five of them (MDA-MB-231, MDA-MB-436, Hs578T, SUM1315, and HBL-100) had a high percentage (˃ 30%) of the CD44high/CD24low immunophenotype with basal/mesenchymal markers or myoepithelial markers but no luminal markers, as well as high levels of expression of the pro-invasive proteins IL-1a, IL-6, IL-8, and urokinase-type plasminogen activator (UPA). This evidence concerns the gene PLAU and breast cancer.