ADO is the chief product from exATP, and ADO receptor A2BR functions as a cell proliferation promoter in human hepatocellular carcinoma (216), prostate cancer (217), colorectal carcinoma (218), breast cancer (219), oral squamous carcinoma (220), head and neck squamous cell carcinoma (HNSCC) (91), and bladder urothelial carcinoma (221). This evidence concerns the gene ADO and head and neck squamous cell carcinoma.