MMP9 and squamous cell carcinoma: After stratifying by tumor histology (squamous cell carcinoma vs. adenocarcinoma), tumor MMP-9 expression was associated with a poor prognosis for relapse (p = 0.003; Figure 2C) and OS (p = 0.033; Figure 3C) and was an independent prognostic factor for relapse (p = 0.035; Table 2) of adenocarcinoma of the lung.