PTEN and breast cancer: Breast cancer cells, in response to endoplasmic reticulum (ER) stress, release exosomes enriched with miR-27a-3p, which are transferred to macrophages and facilitate tumor immune evasion by enhancing PD-L1 expression through the phosphatase and tensin homolog (PTEN)/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway (7).