Constitutively, activated tyrosine (Y705)-phosphorylated STAT3 (p-STAT3) has been demonstrated in many human breast [12] and lung [7] cancer cell lines, in 40–50% of primary human breast cancers [12,19], and 22–65% of non-small cell lung cancers [20], making it an attractive target for the development of anti-cancer therapies. This evidence concerns the gene STAT3 and breast cancer.