ADORA2A and head and neck squamous cell carcinoma: Together these preclinical findings have led to the A2AR antagonists PBF-509 (NCT02403193) and CPI-444 (NCT03337698) being trialed for safety and efficacy against HNSCC, NSCLC, melanoma, renal cell cancer, triple-negative breast cancer (TNBC), colorectal, bladder, and prostate cancers [212].