HAVCR2 and osteosarcoma: Various immunotherapies have been investigated for the management of osteosarcoma since osteosarcoma tumours frequently express high levels of key immune checkpoint inhibitor proteins (namely programmed cell death protein 1 (PD-1), programmed death-ligand 1 (PD-L1), Cytotoxic T-lymphocyte associated protein 4 (CTLA4), and T-cell immunoglobulin and mucin domain 3 (TIM3)) (14–17).