MMP9 and cancer: It has been reported that metastasis is the major problem in lung cancer and the CBX family could play a significant role in controlling the migration of cancer cells.21 MMP2 and MMP9 are capable of degrading type IV collagen, which induces cancer cell metastasis via promoting the primary tumour to migrate. 37 Meanwhile, CXCR4 was reported to be a marker protein of metastasis in gastric cancer cells.38 In this study, we firstly proved that CBX4 knockdown significantly inhibited the wound closure in scratch migration assay and cell invasion in transwell assay (Figure 5A‐D).