Release of clotting factors from photosensitized endothelial cells: a possible trigger for blood vessel occlusion by photodynamic therapy.

Photodynamic treatment of solid tumors results in the occlusion of blood vessels in the treated tissue. We hypothesize that this process is triggered by the release of one or more clotting factors from the photodamaged endothelial cells. Experimental evidence is presented that immediately after photodynamic treatment, cultured endothelial cells start releasing clotting factors into the medium in a dose range of minimal cytotoxicity.