Similar research efforts have been made in dogs, and previous studies have revealed that tumor-infiltrating lymphocytes collected from OMM express the immunosuppressive receptor PD-1 on their surface, and PD-L1, a ligand for PD-1, is expressed in the tumor tissues of OMM at a high rate (73–100%) [17,18,19,20]. Here, CD274 is linked to neoplasm.