Photodynamic therapy (PDT) should win the beauty contest between the differing endoscopic treatments for malignant or premalignant gastrointestinal mucosa with ease. The name could have been dreamed up by an advertising agency and the technique is based on the elegant theoretical advantage of dual selectivity resulting from the combination of a designer drug and laser light. Throw in local oxygen radical induced cytotoxicity and several unique safety features and you have an unbeatable product. However, although there is increasing interest in the use of PDT in gastroenterology, it is not new and remains experimental.

The initial step in PDT is the administration of a photosensitiser, most of which have been based on porphyrins. The photosensitiser is inert until activated by light, when localised cytotoxicity is produced—due to the production of oxygen radicals with most agents that have been used. An additional property of several photosensitisers has been their preferential retention in different tissues, particularly mucosa or neoplasms. By endoscopy most of the lesions suitable for PDT can be reached through the intestinal lumen and laser light directed at the abnormal area with sparing of adjacent normal mucosa. PDT possesses an important advantage over other techniques of tissue ablation, especially thermal destruction, in that while there is cytotoxicity and tissue necrosis, collagen remains intact,1 and hence the risks of perforation are reduced.2 Sunlight will also activate photosensitisers causing skin photosensitivity which has been the principal side effect of treatment and patients need to avoid natural light until the drug has been cleared. The other disadvantage of PDT is the limited penetration of light into tissue which restricts treatment to a depth of 10 …