STAT3 and lung cancer: Similar to tumor tissues, the expression of p53 and its target proteins (p21 and BAX), and cleaved caspase 3 were increased, whereas the phosphorylation of STAT3 was decreased in the Chi3L1 knockdown lung cancer cells than those of the lung cancer cells transfected with control siRNA (Fig. 3c and Additional file 1: Figure S2A-F).