PDTs

PDTs, or photodynamic therapy, are medical treatments that combine a photosensitizing drug with light exposure to destroy targeted tissue. The approach relies on three elements: a photosensitizer, light of a specific wavelength, and tissue oxygen. After administration, the photosensitizer tends to accumulate more in abnormal or diseased tissue than in normal tissue.

When the targeted area is illuminated, the photosensitizer becomes activated and transfers energy to molecular oxygen, generating reactive oxygen species such as singlet oxygen. These reactive molecules damage cellular components, leading to cell death, disruption of tumor blood vessels, and an inflammatory response that can aid in tumor control. The depth of effect is influenced by the light wavelength and tissue characteristics, which determine how deeply the light penetrates.

PDTs are used to treat various cancers and precancers, particularly those on or near surfaces such as the skin, mucous membranes, or the linings of hollow organs (for example, esophagus, airways, and bladder). In ophthalmology, photosensitizers like verteporfin are used in light-activated therapy for certain retinal diseases. Common photosensitizers include porfimer sodium, benzoporphyrin derivatives, and temoporfin, among others, with regimens tailored to the site and condition being treated.

Limitations include photosensitivity lasting days to weeks after treatment, restricting exposure to bright light; variable depth penetration that favors superficial lesions; and dependence on adequate tissue oxygenation. Side effects are related to treatment area and may include local pain, inflammation, swelling, or transient organ-specific changes.