Moreover, hsa_circ_0001649 was involved in the E2-mediated upregulation of MMP9 in ESCs and ThESCs, suggesting that hsa_circ_0001649 functions as a migration–invasion suppressor in EMs, which is consistent with its function in colorectal cancer, gastric cancer and hepatocellular carcinoma (Qin et al. 2016, Li et al. 2017a, Ji et al. 2018). Here, MMP9 is linked to gastric cancer.