Fig. 3

Effect of sEVs on the pre-metastatic niche in breast cancer. An overview of the effects of sEVs on the PMN of breast cancer can be summarized as follows: inflammation, immunosuppression, angiogenesis and vascular permeability, stromal remodelling and organotropism. a The sEVs secrete inflammatory factors, such as IL-6 and IL-8, promoting angiogenesis and recruiting immunosuppressive cells to promote the formation of breast cancer PMNs. In turn, inflammatory molecules can affect the distribution of sEVs and thus influence the PMN. b The sEVs not only inhibit T cells and induce immune escape by transporting PD-L1, but also exert immunosuppressive effects by recruiting MDSCs, altering DC cell activity, and transforming macrophages. sEVs also stimulate immune cells such as TANs to secrete cytokines, which suppress the antitumour immunity. c Through proangiogenic factors, including MMPs, and VE-cadherin, as well as miRNAs, sEVs are believed to act on angiogenesis and vascular permeability in the PMN of breast cancer. d In breast cancer, sEVs facilitate the turnover of CAFs to remodel the ECM and create the PMN. e The sEVs of breast cancer can provide a measure of organtropism, such as specific exosomal integrin combinations (there is a link between exosomal α6β4 and α6β1 integrins and lung metastasis/exosomal αvβ5 integrin with liver metastasis/exosomal αvβ3 integrin with brain metastasis). In addition, exosomal IBSP and miRNAs are involved in breast cancer brain metastasis