CD274 and neoplasm: TDEs secreted by primary tumour cells could induce tissue resident interstitial macrophages (IM) in the premetastatic niche to upregulate the immunosuppressive molecule programmed death ligand 1 (PD-L1) and secrete a large amount of lactic acid, thereby establishing an immunosuppressive microenvironment to promote solid tumour metastasis [117].