STAT3 and breast cancer: To determine if any of the selective Stat3 compounds induce apoptosis and whether or not apoptosis induction is selective for tumor cell lines with constitutive Stat3 activation, we examined each of our Stat3 selective compounds for the ability to induce apoptosis of breast cancer cell lines, MDA-MB-231 [36]–[38], MBA-MB-468 [33], [39], [40] and MDA-MB-435 [33], [39] with constitutively active Stat3 and two breast cancer cell lines, MDA-MB-453 [17], [33], [39] and MCF7 [17], without constitutively active Stat3.