Extracellular adenosine, which accumulates due to tissue hypoxia, also contributes to ICP/ICP-L upregulation (59), and adenosine levels are significantly higher in the BM of myeloma due to the highly coordinated expression of adenosinergic ecto-nucleotidases (CD39/CD73/CD38/CD203a) strategically located at the interface between myeloma cells and neighboring cells (60). This evidence concerns the gene ENTPD1 and plasma cell myeloma.