PDT: What's Past Is Prologue

Despite descriptions of light-mediated therapy in ancient texts and the discovery of photodynamic therapy (PDT) in the early 1900s, the landmark article in 1978 in Cancer Research by Dougherty and his colleagues at the Roswell Park Cancer Institute remains rightly viewed as the starting point for clinical PDT in modern medicine. As a large clinical series that explored many of the factors now viewed as critical determinates of PDT dose, efficacy, and toxicity, that study showed remarkable foresight, yet it also served to raise as many questions as it answered. Since its publication, PDT has been increasingly utilized in clinical practice for the treatment of both benign and malignant conditions, and many of their questions have yielded new technologies and areas of investigation, thus remaining highly relevant nearly 40 years after their initial asking. Moreover, continuing advances in our ability to measure physical properties such as absorbed light dose, photosensitizer concentration, tissue oxygen concentration, and singlet oxygen production in real-time may allow for adaptive modification of light delivery during PDT on a fine scale to optimize treatment response. Finally, combining molecularly targeted drugs and novel photosensitizers has the potential to improve further the therapeutic index and extend the spectrum of clinical PDT far beyond what was imagined when that sentinel manuscript was written. (C) 2016 AACR.