STAT3 and lung cancer: Although the majority of studies described STAT3 as an oncogene, STAT3 also possesses tumor suppressive activity in a variety of solid cancers, such as brain, colorectal, pancreatic, thyroid, prostate and lung cancer, thereby complicating efforts to successfully implement STAT3 axis targeting into clinics [20,29,117,118,119,120,121,122,123,124,125].