Liver cancer is associated with chronic inflammation, which is linked to immune dysregulation, disordered metabolism, and aberrant cell proliferation. Nucleoside triphosphate diphosphohydrolase-1; (CD39/ENTPD1) is an ectonucleotidase that regulates extracellular nucleotide/nucleoside concentrations by scavenging nucleotides to ultimately generate adenosine. These properties inhibit antitumor immune responses and promote angiogenesis, being permissive for the growth of transplanted tumors. Here we show that Cd39 deletion promotes development of both induced and spontaneous autochthonous liver cancer in mice. Loss of Cd39 results in higher concentrations of extracellular nucleotides, which stimulate proliferation of hepatocytes, abrogate autophagy, and disrupt glycolytic metabolism. Constitutive activation of Ras-mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR)-S6K1 pathways occurs in both quiescent Cd39 null hepatocytes in vitro and liver tissues in vivo. Exogenous adenosine 5′-triphosphate (ATP) boosts these signaling pathways, whereas rapamycin inhibits such aberrant responses in hepatocytes. Conclusion: Deletion of Cd39 and resulting changes in disordered purinergic signaling perturb hepatocellular metabolic/proliferative responses, paradoxically resulting in malignant transformation. These findings might impact adjunctive therapies for cancer. Our studies indicate that the biology of autochthonous and transplanted tumors is quite distinct. (HEPATOLOGY 2013)