ADORA2A and head and neck squamous cell carcinoma: A phase I clinical trial (NCT02655822) of an A2AR antagonist (PBF-509 and CPI-444) alone or with a PD-L1 inhibitor, atezolizumab, has also been performed to evaluate the clinical efficiency of A2AR blockade for solid tumors, e.g., HNSCC [206].