Virtually all solid tumors are dependent on a vascular network to provide them with the right amount of nutrients and oxygen. In that sense, low oxygen tension or hypoxia leads to an adaptive response that is transcriptionally regulated by the hypoxia-inducible factors (HIF), which are tightly controlled by the HIF prolyl hydroxylases (PHD). In this study, we show that inhibition of the oxygen sensor PHD2 in tumor cells stimulates vessel formation but paradoxically results in a profound reduction of tumor growth. This effect relies on the antiproliferative nature of the TGFβ signaling pathway, in a largely HIF-independent manner. Moreover, our findings reveal that PHD2 has an essential function in controlling the dual nature of TGFb during tumorigenesis and may offer an alternative opportunity for anticancer therapy.