We then applied western blot assay to further prove that the ERα/CCL2 axis in lung cancer cells can affect MMP9 production, and results showed that adding CCL2‐shRNA or CCL2‐cDNA (see western blot analysis in Fig. 4D) can lead to reverse the effect on production of MMP9 from THP‐1 cells cocultured with A549 cells (Fig. 4J left) or H1299 cells (Fig. 4J, right). Here, MMP9 is linked to lung carcinoma.