NT5E and neoplasm: In more detail, release of ATP through exocytosis or Pannexin-1 channels and subsequent CD39/CD73-dependent extracellular degradation to adenosine contribute to the accumulation of non-physiologically high levels of adenosine in the tumor microenvironment, particularly in hypoxic tumors that may reach extracellular concentrations in the μM range (0.2 to 100 μM) compared to 10–300 nM in normal tissues [74,121,122,126,127].