Our in vivo data on BC xenografts treated with thiostrepton not only validated our in vitro findings by causing regression of tumor size and volume via down-regulation of FoxM1 and its downstream targets; VEGF, MMP-9, MMP-2, Bcl-xL and XIAP, but also gave an indication that thiostrepton can be used in humans as the doses of thiostrepton used did not induce toxicity, weight loss or lethargy in the experimental animals. This evidence concerns the gene FOXM1 and breast cancer.