The role of light in the treatment of non-melanoma skin cancer using methyl aminolevulinate

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Abstract
Photodynamic therapy (PDT) is a developing approach to the treatment of cancer and other diseases that involves the use of light to activate photosensitizer molecules. The light energy absorbed by the photosensitizer is transferred to molecular oxygen, which is converted into the highly reactive and cytotoxic species, singlet oxygen. Topical agents such as aminolevulinic acid (ALA) or methyl aminolaevulinate (MAL) may be used for PDT of non-melanoma skin cancers (NMSC) because, in vivo, these agents stimulate the production of porphyrins which act as powerful photosensitisers. This brief review focuses on the use of light to activate MAL, which is now an approved drug (Metvix for certain NMSCs in the European Union. Porphyrins produced by the action of MAL can be activated using red light, which is also capable of deeply penetrating the skin. A number of light sources are available for treatment of NMSC using MAL, including very convenient non-laser sources such as non-coherent filtered lamps and, more recently, sources containing arrays of light-emitting diodes (LEDs). The Aktilite lamp, specifically designed for use with Metvix cream, has an emission spectrum that closely matches the red light absorption profile of PpIX.