Photodynamic therapy and diagnosis: Principles and comparative aspects.

13 Feb 2018

Photodynamic therapy (PDT) is an evolving method of treating superficial tumours that is 20 non-invasive and carries minimal risk of toxicity. PDT combines tumour-selective photosensitiser 21 dyes, tissue oxygen and targeted illumination to generate cytotoxic reactive oxygen species (ROS) 22 within the tumour. In addition to directly acting on tumour cells, PDT damages and restricts tumour 23 microvasculature, and causes a local inflammatory response that stimulates an immune response 24 against the tumour. Unlike surgery or radiotherapy the surrounding extracellular matrix is 25 unaffected by PDT, thus tissue healing is excellent and PDT seldom scars. This, combined with the 26 ease of light application, has made PDT a popular treatment for cancers and pre-cancers in humans. 27 Moreover, because photosensitiser dyes are fluorescent and selectively accumulate in tumour 28 tissues, they can additionally be used to visualise and discriminate tumour from normal tissues, 29 thereby improving the accuracy of tumour surgery. 30 31