GPX4 and neoplasm: Among the main mechanisms preventing the cytotoxic effects of PDT, the following elements might play an important role: (1) altered genetic profile, and particularly altered expression of tumor survival genes [177–179], (2) increase in DNA damage-repair processes [180], (3) increase in AKT/mTOR signaling, (4) expression of ROS-scavenger proteins (e.g., glutathione S-transferase (GST), glutathione peroxidase 4 (GPx4)) [181, 182], and generation of nitric oxide (NO) [183, 184].