Besides, thyroid cancer cells upregulated negative immune checkpoints, such as CTLA-4 (cytotoxic T-lymphocyte associated protein 4) and PD-L1 (programmed death-ligand 1), as well as immunosuppressive enzymes (IDO1, indoleamine 2,3-dioxygenase 1). This evidence concerns the gene CTLA4 and thyroid cancer.