MMP9 and lung carcinoma: Here, we mainly explored the effect of circDENND4C, miR-200b, and MMP-9 in the progression of lung cancer, and from the overall results of this study, it was found that (1) circDENND4C, miR-200b, and MMP-9 have significant changes in NSCLC cell lines (2); the sequential targeted regulatory relationship among circDENND4C, miR-200b, and MMP-9 was firstly confirmed; and (3) circDENND4C, miR-200b, and MMP-9 were involved in the changes of biological behavior of lung cancer cells, including cell proliferation, cell cycle, apoptosis, migration, and invasion.