History of PDT

This chapter presents the brightest historical milestones behind the development of photodynamic therapy (PDT). We initially present how photodynamic reactions were first observed by scientists from three different countries in the beginning of the twentieth century. Oskar Raab, from Germany, observed by accident that protozoan cells stained with fluorescent dyes were killed upon illumination, while Prime, in France, reported that human subjects who ingested also fluorescent dyes for an experimental treatment of neurological diseases developed severe erythema after short exposure to sunlight. Niels Finsen, from Denmark, was awarded with the third Nobel Prize of Medicine in the history for the development of light-based treatments for skin infections. Following, we describe how PDT slowly evolved until the 1960-1970s when new generations of less toxic photosensitizers were developed for diagnosis and treatment of solid tumors. Only then PDTreally became a hot scientific area that began to attract many researchers to the field. We also describe the first huge medical and economic impact that PDT as the first effective treatment for age-related macular degeneration, the leading cause of adult blindness in the world. Finally, we go through the main discoveries in veterinary medicine over the past years for the treatment of localized tumors and infections in diverse animal species.