TGFB1 and gastric cancer: Alternatively, gastric cancer-derived exosomal miR-21-5p that targets SMAD7, an inhibitor of TGF-β signaling, has been shown to promote mesenchymal transition of peritoneal mesothelial cells, a process that promotes invasion through matrix remodeling and angiogenesis of the peritoneum (Li et al., 2018).