As a transcription activator and an oncogene, STAT3 which is frequently detected with persistent activation in most human cancer cell lines and tumor tissues, is crucial in tumor cell proliferation, invasion, and migration, and is capable of inducing epithelial–mesenchymal transition (EMT), regulating the tumor microenvironment and promoting CSCs self-renewal and differentiation which all benefit the progression of cancer. Here, STAT3 is linked to neoplasm.