CD274 and osteosarcoma: Yet, upregulation of programmed cell death-1 receptor (PD-1) on CD8(+) tumor-infiltrating lymphocytes (TILs) and interaction with its ligands (PD-L1 and PD-L2) in tumor cells are proven immune escape routes to impede anti-tumor activity of T cells against osteosarcoma [16, 17].