On the contrary, it has been shown that the transfection of HPV E6/E7 oncogenes in HNSCC cells induce ROS production via NADPH oxidase 2 (Nox2), another source of ROS generation that does not involves electron leakage in the mitochondrial ETC, which increases radiosensitivity in HPV-positive HNSCC (Figure 1) [46]. This evidence concerns the gene CYBB and head and neck squamous cell carcinoma.