MMP9 and lung cancer: MMP‐9 (gelatinase‐B) is the most important of MMPs which degrades the type IV collagen and is highly active in many cancer cells, such as breast, brain, prostate, and lung cancer (Alaseem et al., 2017; Gialeli et al., 2011; Gong et al., 2016; Nelson, Fingleton, Rothenberg, & Matrisian, 2000).