MMP9 and esophageal squamous cell carcinoma: As a proof of concept, Wang et al. showed that let-7i mimics of 22 base pairs (bps) in length potently inhibit the growth and migration of A549 cells, results that are consistent with those from Ling et al., who demonstrated that let-7a-mimic treatment hinders epithelial–mesenchymal transition, cell mobility, and expression of VEGF-C and MMP9 in esophageal squamous cell carcinoma (ESCC) cells [74,75].