Of all human MMPs described so far, gelatinases (or type IV collagenases), i.e., MMP-2 (gelatinase-A) and MMP-9 (gelatinase-B), are recognized to be apparently correlated with pathological grading, staging, metastasis, and poor prognosis in patients with lung adenocarcinoma [31,32]. This evidence concerns the gene MMP9 and lung adenocarcinoma.