STAT3 and breast cancer: Activation of STAT3 promotes cell survival and growth, whereas treatment with a STAT3 inhibitor reduces the level of STAT3 and expression of its target genes, such as Bcl-xL, cyclin D2, and VEGF. Hypoxic conditions induce expression and/or serine phosphorylation of STAT1, STAT3, and STAT5 in breast cancer MCF7 cells [65].