CD274 and breast cancer: The approach generally taken so far was to knock-out/knockdown PD-L1 expression in breast cancer cells or to inhibit it by antibodies; such studies have shown that down-regulation of PD-L1 has led to inhibition of tumor cell proliferation and migration, to reduction in EMT-related properties of the cells and to the expression of CSC-related properties [31,32,33,34].