Signal transducer and activator of transcription 3 (STAT3) regulates the expression of genes important for essential cellular processes including survival, proliferation, self-renewal, angiogenesis, and immune response. As an early tumor diagnostic marker, it is considered that constitutive STAT3 activation is a sufficient factor to cause malignant transformation and tumor development in model systems. The classical IL-6/STAT3 signaling pathway in cancer cells. IL-6 binds to the membrane-bound IL-6 receptor α (IL-6R) and IL-6 receptor β (also known as gp130). The IL-6/IL-6R/gp130 complex activate the phosphorylation of JAKs, followed by STAT3 phosphorylation and activation. Then, phosphorylated STAT3 forms a homodimer and translocates into the nucleus to bind to the promotor region of target genes and activates target gene transcription.