The selective toxicity of the SOD-mimetic MitoTEMPO (Fig 3A), a mitochondria-targeted substance that increases mitochondrial hydrogen peroxide, further supports our hypothesis, that i) the melanoma cells are more susceptible to increased H2O2 levels in context of cell death, and ii) a major source of the higher ROS level in tumor cells appears to be mitochondria. The gene discussed is SOD1; the disease is melanoma.