CD274 and breast carcinoma: ER stress promotes exosome secretion and increased exosomal miR-27a-3p, which can promote immune escape by upregulating PD-L1 via the membrane-associated guanylate kinase, WW and PDZ domain-containing (MAGI1)/phosphatase and tensin homolog (PTEN)/phosphoinositide-3 kinase (PI3K) axis in breast cancer (35).