In a follow-up study, the authors showed that NOX4 (NADPH oxidase subunit 4) was a critical mediator of radio resistance exerted by cyclic hypoxia (0.5–1% O2, 10 min hypoxia, 10 min reoxygenation, 12 cycles) in glioblastoma cell lines, GBM8401 and U251 and tumor models. Here, NOX4 is linked to neoplasm.