ENTPD1 and neoplasm: In this pathway, nucleotides (ATP and ADP) released by a variety of cell types in response to stress signals such as injury, hypoxia and inflammation, which commonly occur in the tumor microenvironment, are jointly hydrolyzed by CD39 ectoenzyme (ENTPD1, ectonucleoside triphosphate diphosphohydrolase-1, EC 3.6.1.5) to generate the respective nucleotides.