PTEN and gastric cancer: Exosomes carrying miR-21 can be transferred from macrophages to GC cells, inhibiting cell apoptosis, enhancing the activation of the PI3K/AKT signaling pathway, and inducing cisplatin resistance by down-regulating PTEN. MiR-21 enhances cell survival by targeting PTEN, inducing resistance to doxorubicin and cisplatin (Yang et al., 2013; Chen et al., 2018b).