Figure 1. Exosomal miRNA-mediated intercellular cross-talk within the tumor microenvironment.

Through intercellular transfer of exosomal miRNA, tumor parenchymal cells can confer drug resistance to each other and enhance the invasiveness of recipient cells. Tumor cells can promote angiogenesis of endothelial cells, and endothelial cells can promote tumor cell proliferation. Immune cells are able to regulate tumor metastasis under different conditions, and tumor cells may induce immune cell dysfunction and pro-inflammatory cytokine release. Tumor cells are capable of inducing CAF phenotype transformation of mesenchymal stem cells, and mesenchymal stem cells can be transferred to the tumor site to promote tumor metastasis or dormancy, but they also inhibit tumor growth in some cases. Adipocytes play an important role in promoting tumor cell invasion, while the effect of tumor-secreted exosomes on adipocytes has not been reported to date. Exosomal miRNA can convert normal fibroblasts into CAFs for tumor survival, and CAFs can promote tumor progression (The direction of exosomal miRNA transfer is denoted by blue arrows; the annotations which are close to the arrows refer to biological effects that are regulated in recipient cells).