Comparison Between the Effect of Tramadol Versus Morphine on PD1 and PD1-ligand in Patients With Chronic Cancer Pain

The use of opioids is the mainstay in the treatment of many types of chronic pain, including cancer and non-cancer-related pain]. Opioids are known to suppress immune function following both acute and chronic administration; however, they appear to be different according to the schedule of administration as well as the state of the organism. Programmed death-1 (PD-1, also known as CD279) belongs to the CD28 receptor superfamily. It is an inhibitory receptor, and its expression is upregulated on activated leukocytes, resulting in an inhibited immune response. PD-1 interacts with two ligands: programmed death ligand-1 (PD-L1, also referred to as B7-H1) and programmed death ligand-2 (PD-L2, also known as B7-DC). PD-L2 is expressed mainly on activated dendritic cells (DCs) and macrophages, whereas PD-L1 is distributed widely. In addition to immune cells, some subsets of tumor cells also express PD-L1 to escape from immunosurveillance. It has been reported that the PD-1/PD-L1 pathway could be activated by surgical stress.