**5. Photodynamic therapy and anti-tumor immunity – A chance for PDT to be more than a local cancer therapy?**

In malignant brain tumors standard therapy is based on surgery, radiation and chemotherapy. The prognosis of patients is still dismal. There is no doubt about the necessitiy of other treatment options. As mentioned in this chapter PDT represents an interesting therapy option in addition to the modern therapeutical strategies described in this book. At the first moment PDT seems only as one additional tool of local tumor treatment, with all advantages, e.g. low costs compared to modern biotechnical products, selective and repetitive application. Therapy resistancy has been seldom observed. PDT is able to occluse tumor associated vessels, mainly PDT induces apoptosis and necrosis, also autophagy plays a role. Great hope lies in the modulation of immune system by PDT. Fluorescence guided tumor resection is able to eradicate tumor locally. In combination with

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induced systemic anti-tumor immune reactions distant tumor cells, e.g. Guerilla cells could be treated. Several mechanisms contribute therefore. Cells killed by PDT produce signals, increasing antigen presentation by dendric cells (DCs) and recruit antigen-specific cytotoxic T lymphocytes (CTLs).(Mroz et al. 2011)

Great importance is also given to so called damage-associated molecular patterns (DAMPs). DAMPs are intracellular molecules in living cells, exposed by sudden cell damage as initialized for example by PDT. Up to date it is generally accepted that PDT activates the immune system. Complete understanding of the processes and how to influence them for improvement the immune responses is mandatory and could be advanced by closer cooperation of researchers in PDT and immunology.
