CD274 and breast cancer: PD-L1 exhibits an anti-apoptotic role in MDA-MB-231 breast cancer cells and silencing PD-L1 in these cells increased cancer cell apoptosis and enhanced cancer cell susceptibility to doxorubicin-induced apoptosis in vitro and in vivo (194), suggesting that PD-L1 not only prevents cancer cell apoptosis, but also promotes chemotherapy resistance.