Thus, progestins appear to promote breast cancer not only by increasing production of the potent mitogenic factor VEGF and stimulating tumor and endothelial cell proliferation (Liang and Hyder 2005), but also by enriching the stem cell-like population, thereby enabling tumors to grow and metastasize (Liang et al. 2010; Horwitz et al. 2013). Here, VEGFA is linked to breast cancer.