Photodynamic Therapy (PDT) is a non‑‑invasive, safe and clinically‑approved procedure that is increasingly been recognized as a promising anticancer therapeutic strategy. The PDT procedure involves the administration of a photosensitizing agent followed by irradiation of the target tissue with light of a specific wavelength, which, in the presence of oxygen, originates a series of photochemical events that lead to the local formation of reactive oxygen species (ROS). Besides the direct effect of ROS, responsible for the selective destruction of tumour cells and vasculature, it is now widely accepted that some PDT protocols can also induce a systemic and tumour‑‑specific immune response. PDT can be very effective against early stage tumours and can also be used as a palliative treatment in advanced cancer patients. There are only minimal side‑‑effects associated with PDT, the most common being temporary skin photosensitivity. No intrinsic or acquired resistance mechanisms are known and the cosmetic outcome after the treatment of skin lesions is very good. Over the last years, great efforts have been made on the development of more effective photosensitizers, on the design of economic and versatile light sources and light delivery devices, and especially on the optimization of PDT protocols that, besides the elimination of the primary tumour, will be able to induce the patient immune system to target and eliminate distant metastasis. With this achievements PDT can move forward to the first line of therapies in the fight against cancer.
