PDL1 is a cell surface immunoglobulin superfamily with two Ig-like domains within the extracellular region and a short cytoplasmic domain. PDL1 is also known as B7-H, B7H1, MGC142294, MGC142296, PD-L1, PDCD1L1 and PDCD1LG1,which is a member of the growing B7 family of immune molecules and is involved in the regulation of cellular and humoral immune responses. PD-L1 provides a molecular stop signal to the adaptive immune system helping to distinguish between self and foreign antigens. PDL1 may inhibit ongoing T-cell responses by inducing apoptosis and arresting cell-cycle progression. Many cancers exhibit upregulated PD-L1 protein expression, and several cancers with high levels of PD-L1 have been associated with increased tumor aggressiveness and poor prognosis. Using new therapeutics that block the PD-L1:PD-1 interaction has proven successful in the clinic for many cancer types and has sparked great interest in the field of cancer immunotherapy.