STAT3 is frequently activated inappropriately in cancer cells, and this is often driven, at least in part, by the presence of cytokines in the tumor microenvironment that can activate this protein, Consequently, there has been an interest in developing cancer therapeutics that block cytokines (either targeting the cytokines themselves or their cognate receptors) or Jak family kinases that are associated with cytokine receptors (Figure 4) (8). This evidence concerns the gene STAT3 and cancer.