Photodynamic therapy (PDT) is an alternative cancer treatment to conventional surgery, radiotherapy and
chemotherapy. It is based on activating a drug with light that triggers the generation of cytotoxic species that promote
tumour cell killing. At present, PDT is mainly used in the treatment of wet age-related macular degeneration, for
precancerous conditions of the skin (e.g. actinic keratosis) and in the palliative care of advanced cancers, for instance
of the bladder or the oesophagus. PDT is still not used as a first line cancer treatment, which is surprising given the
first clinical trials by Dougherty’s group dating back to the 1970’s. PDT has significant advantages over surgery or
radiation therapy for low lying tumours due to better cosmetic outcome and localised treatment for the patients.
However, despite these advantages and significant developments in optical technology that has enabled light
penetration to deeper lying tumours, in excess of 5 cm, a lack of phase III clinical trials has slowed down the uptake of
PDT by the healthcare sector as a frontline treatment in cancer. However research continues to demonstrate the
potential benefits of PDT and the need to stimulate funding and uptake of clinical studies using next generation
photosensitizers offering advanced targeted delivery, improved photodynamic dose combined with modern light
delivery technologies. This review surveys the available PDT treatments and emerging novel developments in the field
with a particular focus on two-photon techniques that are anticipated to improve the effectiveness of PDT in tissues at
depth and on next generation drugs that work without the need of the presence of oxygen for photosensitization
making them effective where hypoxia has taken hold.