CD274 and neoplasm: Bioactive lipid prostaglandin E2 (PGE2), a derivative of arachidonic acid, can be produced by MDSCs and increases stem cell-like properties, as well as PD-L1 expression in epithelial ovarian cancer (71).PEG2 also regulates PD-L1 expression in MDSCs via COX2/mPGES1/PGE2 pathway, which reprograms PGE2 metabolic pathways in TME and provides an opportunity to reduce tumor immune suppression (72).