CD274 and cancer: In addition, hypoxia and epigenetic mechanisms also present within the tumor environment regulate PD-L1 expression.48–50 For example, the expression of microRNA 513 down-modulates PD-L1 mRNA translation in human cholangiocytes,51 while microRNA 152 performs a similar function in gastric carcinoma.52 Several cancer cell types disrupt the structure of the PD-L1 mRNA 3′UTR to constitutively increase PD-L1 expression.53