The Skin Cancer Foundation Journal

MAY 2012

The 2012 edition of The Skin Cancer Foundation Journal features medically reviewed, reader-friendly articles such as tanning, the increasing incidence of skin cancer diagnoses among young women, & the prevalence of melanoma among white males over 50.

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Page 64 of 103

Photodynamic Therapy A New Frontier in Early Skin Cancer Treatment JESSE M. LEWIN, MD, JULIE K. KAREN, MD, and ELIZABETH K. HALE, MD P hotodynamic therapy (PDT) has become an increasingly important tool in the derma- tologist's arsenal of treatments for skin diseases ranging from pre- cancers (actinic keratoses, or AKs) to acne. The process was first described in 1900 by medical student Oscar Raab, who observed that sunlight, when combined with a fluorescent dye, could kill single-celled organisms known as paramecia.1 The discovery was serendipitous: Raab noted that the dye's ability to kill the organisms was most pronounced at midday when the amount of natural sunlight in the laboratory was greatest; the dye was least effective when the experiment was conducted in the dark. Several years later, the term "photodynamic therapy" (PDT) was coined by Raab's mentor, Professor Hermann Von Tappeiner, who investigated the use of sunlight and arc lamps in conjunc- tion with fluorescent dyes to treat skin cancer, skin problems associated with lupus, and warts.2 PHOTOSENSITIZERS PDT requires a light source, a pho- tosensitizer (a drug that becomes activated by light), and the oxygen in human tissue. The photosensitizer is first applied to the skin lesions, which preferentially take up much more of the drug than the surrounding normal tissue does. When the photosensitized area is exposed to the light, it triggers the lesion to produce oxygen molecules (oxygen free radicals) that destroy the cancerous tissue while sparing most of the surrounding unaffected skin. Photosensitizers can be administered topically, orally, intravenously, or injected, depending on the disease. The two most commonly used topical photosensitizers for PDT in the United States are 5-aminolevu- linic acid hydrochloride (ALA) and its related compound, methylami- nolevulinate (MAL). ALA is typically applied to the skin in the form of a 20 percent solution (Levulan® ). MAL is available as a 16.8 percent cream (Metvix® ). Choice of photosensitizer depends on the patient and skin lesions being treated. LIGHT SOURCES Sunlight is not a PDT light source, of course, because its ultraviolet (UV) rays can lead to skin cancer over time, defeating the purpose of the therapy. Lasers work quickly, minimizing therapeutic exposure time. A 40-year-old patient with a history of actinic keratosis and basal cell carcinoma undergoing topical photodynamic therapy using blue light. 63

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