The bystander effect in tumor response to photodynamic therapy (here we go again)

In last several years there was an emergence of evidence pertaining to several important candidates for powerful mediators of PDT-induced bystander effect. This includes a better knowledge of PDT-triggered lipid peroxidation propagation and its potential for spreading over considerable distances over extended duration. Importantly, there is a direct link between lipid peroxidation cascade and the infliction of PDT-mediated ferroptosis. The latter is notorious for its capacity for the induction of large-scale cell death spreading over large tumor regions in propagative trigger waves. PDT-induced bystander effect in tumors may turn out to have a considerable relevance for clinical outcome.