ENTPD1 and neoplasm: Hypoxia also drives expression of the well-defined transcription factor HIF1α, which promotes the expression of ectoenzymes CD39 (NTPDase1) and CD73 (5’-NT) on tumor cells, stromal cells, and tumor infiltrating immunosuppressive cell subsets such as regulatory T cells (Treg) and myeloid derived suppressor cells (MDSC) [16,17].