MMP9 and esophageal squamous cell carcinoma: After co‐overexpression of LCN2/LOXL2, LCN2/MMP9, and LOXL2/MMP9, the phosphorylation levels of NF‐κB, STAT3, and PTEN still remained unchanged, while the phosphorylation levels of FAK, AKT, and GSK3β increased, suggesting that LCN2/LOXL2/MMP9 protein–protein interactions promoted migration and invasion of ESCC cells by activating the FAK/AKT/GSK3β signalling pathway (Fig. 7B).