photodynamic therapy

Photodynamic therapy is based on the pathological
processes that underpin the photosensitivity seen in
porphyria, i.e. the presence of potent endogenous photosensitisers which results in tissue damage when exposed
to light. In photodynamic therapy, topical photosensitisers are applied to the tumour, which is subsequently
exposed to visible light. Some tumours may selectively
absorb the photosensitiser, thus enhancing the therapeutic ration. Photodynamic therapy is particularly useful
for relatively flat lesions, such as some intra-epithelial
carcinomas and superficial basal cell carcinomas, and
may be preferable to surgery or other treatment. The
treatment is time-consuming, as the sensitiser needs to
be applied for several hours before exposure to the light
source; as with porphyria, exposure may be painful.