Photodynamic therapy (PDT) serves as a multifaceted treatment primarily targeting pre-cancer changes of the skin, e.g., Actinic Keratosis and, in certain situations, superficial skin cancers. Its effectiveness extends to conditions like actinic keratoses, in situ squamous cell carcinoma (Bowen disease), and superficial basal cell carcinomas. In certain cases, it also addresses small, thin, low-risk nodular basal cell carcinomas located outside the head and neck region.
Beyond its conventional applications, PDT finds its use in off-label treatments, offering facial rejuvenation and addressing mild to moderate acne. Its therapeutic scope also encompasses various skin infections, including wound infections, onychomycosis, viral warts, and cutaneous leishmaniasis. The treatment’s potential is further explored in conditions like psoriasis, mycosis fungoides, and extramammary Paget disease.
The mechanism of PDT hinges on the use of photosensitising agents, oxygen, and light. These elements converge in a photochemical reaction that targets and eradicates cancer cells. Photosensitising agents are introduced into the body through topical, oral, or intravenous routes. Once administered, these agents accumulate in cancer cells and activate under specific light wavelengths. This activation triggers a photodynamic reaction, producing reactive oxygen species such as singlet oxygen, hydroxyl radicals, and superoxides, which interact with cellular structures leading to cell death.
The spectrum of photosensitising agents includes Methyl aminolevulinic acid cream, known for its use in treating actinic keratoses and superficial basal cell carcinoma. This cream, compatible with red light or daylight, ensures cutaneous photosensitivity resolves within a day post-application. Similarly, Aminolevulinic acid hydrochloride topical solution, approved in the USA for actinic keratoses treatment, pairs with blue light. The BF-200 ALA gel, also authorized in the USA for actinic keratoses treatment, incorporates a nanoemulsion formulation and is used with red light, specifically BF-RhodoLED. Porfimer sodium, administered intravenously, leads to prolonged cutaneous photosensitivity, while Benzoporphyrin derivative monoacid ring A represents the second-generation photosensitisers currently under evaluation. Other agents like Tin ethyl etiopurpurin and Lutetium texaphyrin are also noteworthy.
PDT employs diverse light sources, including laser, nonlaser, and ambient daylight. Laser light, characterized by its monochromatic, coherent, and intense nature, is apt for treating small skin lesions. Nonlaser light, emitting polychromatic light, caters to the treatment of larger skin lesions and is cost-effective compared to laser sources. Ambient daylight, although free and readily available, requires careful consideration regarding exposure duration, reliability, and intensity based on location and season.
The application of PDT encompasses various skin conditions such as actinic keratoses, acne, basal cell carcinomas, cutaneous leishmaniasis, intraepidermal squamous carcinoma, squamous cell carcinoma, mycosis fungoides, Kaposi sarcoma, onychomycosis, psoriasis, and viral warts. The administration of PDT involves multiple stages, starting with potential skin preparation through gentle scraping or needling to enhance drug absorption. Following the application of the photosensitising drug, a waiting period allows for drug concentration in cancer cells. The treatment then proceeds with light exposure, varying in duration based on the light source used. After treatment, the area is protected from further light exposure, and a second treatment cycle may follow after 7–10 days if necessary. The healing process involves a sunburn reaction, typically resolving within 4 to 8 weeks. Recent studies suggest that pre-treatment with high dose oral vitamin D could enhance the effectiveness of topical PDT.
While PDT is generally well-tolerated, potential side effects stem from light sensitivity of the treated area, lasting about 24 hours depending on the specific agent used. Side effects may include sensations of burning or stinging, swelling, redness, crust formation, itchiness, peeling, blistering, and potential skin infections. To mitigate discomfort during the procedure, local anesthetics like lignocaine spray may be applied. Post-treatment, the treated skin lesion may blister and ulcerate as cancer cells die, leading to healing over several weeks with minimal scarring, although pigment changes may occur. It’s essential to acknowledge that while photosensitising drugs target cancer cells, they can also increase light sensitivity in healthy cells, necessitating protective measures against light exposure for a defined period, especially when the drugs are administered systemically.
Centre for Medical and Surgical Dermatology offers unique and personalized photodynamic therapy treatment options for each patient to treat various skin conditions like acne and actinic keratosis.
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