ADO and neoplasm: CD39/ecto-nucleoside triphosphate diphosphohydrolase-1 (ENTPDase1) is the dominant ecto-nucleotidase broadly expressed on immune cells, endothelial cells (ECs) and tumor cells, which drives the sequential hydrolysis of ATP and ADP to AMP [3]. The formation of AMP to ADO is accomplished primarily through ecto-5-nucleotidase (CD73), a glycosyl phosphatidylinositol-linked membrane protein, also expressed on various immune cells, ECs and tumor cells [4].