STAT3 and cancer: Signal transducer and activator of transcription 3 (STAT3) is known to promote tumor cell proliferation, survival, and invasion [1,2], mediate procarcinogenic inflammation while suppressing the host’s antitumor immunity [3], induce cancer stem cell renewal [4,5,6], enhance epithelial-mesenchymal transition [7,8] and angiogenesis [9,10], and generate positive autocrine and paracrine feedback loops between tumor cells and their microenvironments [11,12] by regulating expression of a number of cancer-related key proteins, cytokines, and growth factors.