In this pathway, the nucleotides adenosine triphosphate (ATP) and adenosine diphosphate (ADP) increase to high concentrations greater than 50 μM in response to stress signals, such as hypoxia, damage, and inflammation in the tumor microenvironment (TME), and are hydrolyzed by the ectoenzyme CD39 (ectonucleoside triphosphate diphosphohydrolase-1, ENTPD1; EC 3.6.1.5) to AMP and subsequently to adenosine (Ado) by the activity of 5′-ectonucleotidase (CD73, EC 3.1.3.5) [8, 9]. The gene discussed is ENTPD1; the disease is neoplasm.