ABSTRACT
Tumor cells escape to immune surveillance(immune escape)is the key factor in the development and progression of tumors. Interaction between the Programmed Death Ligand 1(PD-L1)on the surface of tumor cells and the Programmed Death-1 (PD-1)receptor on cytotoxic T lymphocytes suppresses the activation of T cells and evendually leads to immune escape and progression of tumors. PD-L1 has two isoforms,membrane-bound form and soluble form. Soluble PD-L1 has been proved to exert biological func-tions by combining with PD-1 as membrane PD-L1. Soluble molecules can affect adjacent cells,also play effective roles in the distance by circulation as cytokines. Thus soluble molecules might play more extensive effects than membrane molecules. In this review,we in-troduced the origin and biological functions of soluble PD-L1 and its clinical significance on diagnosis and prognosis of malignant tumors.