HIF1A and glioblastoma: In vitro and in vivo experiments done using U87 glioblastoma multiforme cells and tumors showed that experimentally imposed cyclic hypoxia (0.5–1% O2, 1 h hypoxia; 30 min reoxygenation; 3 cycles) increased HIF-1α signaling and enhanced its stabilization in a ROS-dependent manner [58].