EPAS1 and neoplasm: Considering that HIF-2 can initiate transcription of VEGF at physiological oxygen concentrations in vitro (Holmquist-Mengelbier et al. 2006), it is plausible that the stem cell-like HIF-2α-positive tumor cells are responsible for VEGF expression and neovascularization in the described tumor areas, possibly contributing to their own perivascular niche.