The protective role of MMP-12, also known as macrophage elastase, in this cohort was surprising since most studies on patients with established lung disease demonstrate elevated MMP-12 as a biomarker of disease severity in COPD patients.[25] Nevertheless, there exists murine data for potential protective roles of MMP-12 in the setting of non-small cell lung cancer.[43] The data is consistent with the hypothesis that after injury, elevated MMP-3 and MMP-12 reduce odds of developing WTC-LI. Here, MMP3 is linked to chronic obstructive pulmonary disease.