Several meta-analyses suggest MMPs as prognostic markers in lung cancer, although the results are conflicting.31, 32, 33 Many previous studies of MMPs comparing lung cancer patients with healthy individuals have also shown contradictory results.34 In our study, a higher level of circulating MMP-8 and MMP-12 was revealed, whereas MMP-2 was reduced in NSCLC compared with COPD patients. Here, MMP12 is linked to lung cancer.