CD274 and neoplasm: Researchers have detected the dynamic changes of PD-L1 expression in the circulatory system by using a liquid biopsy technique, including soluble PD-L1 (sPD-L1), exosomal PD-L1 (exoPD-L1), blood PD-L1 mRNA, and PD-L1 expression in circulating tumor cells (PD-L1+CTCs) (Figure 2).