[Microcirculatory effects of photodynamic therapy with hematoporphyrin derivative]

Hematoporphyrin derivative photosensitizes selectively malignant tumors following intravenous administration and shows typical fluorescence patterns in the range between 630 nm and 690 nm. Irradiation with laser light (630 nm) causes selective tumor necrosis due to a phototoxic effect. The site of action of this "photodynamic treatment (PDT)" remains obscure. In this study it could be demonstrated that directly after PDT a selective haemorrhage and thrombosis of blood vessels occurs in the tumor tissue. Furthermore, the arterioles of the surrounding normal tissue constrict completely. Venules of normal tissue showed slow thrombosis. Basically, the result of photodynamic treatment was a complete breakdown of tumor tissue microcirculation accompanied by partial damage to the surrounding normal tissue perfusion. This evaluation of the impact of PDT on tumor microcirculation led to the conclusion that a primary site of action of photodynamic therapy may contribute to the selective destruction of tumor microcirculation.