Our hypotheses can not only explain why iron addition decreased but not increased the cytotoxicity of DHA in some cells, but also explain why DHA selectively kills cancer cells: (1) cancer cells express higher level of TfR1 [17], thus show more susceptible to DHA than normal cells; (2) cancer cells need excess iron for rapid proliferation, so iron deficiency is more toxic to cancer cells than to normal cells [17], [20]. This evidence concerns the gene TFRC and nutritional disorder.