We excluded duplicates (n = 2), letters, reviews or meta-analysis (n = 16), nonhuman studies (n = 27), studies not related to research topics (n = 30), noncase-controlled or cohort studies (n = 7), studies not relevant to MMP-7 protein studies (n = 10), studies not relevant to lung cancer (n = 13) and studies that did not supply enough information (n =2). This evidence concerns the gene MMP7 and lung cancer.