ADORA2A and neoplasm: With respect to receptors/ligands, tumor-induced immune tolerance is mediated by changes in the expression of several inhibitory checkpoints including CTLA-4 [40,41,42], PD-1, and its ligand (PD-L1) [43], LAG-3 [44], TIM-3 and its ligand (galectin-9) [45], and adenosine A2a receptor (A2aR) [46].