Multicentre randomized controlled studies demonstrate high clearance rates with topical photodynamic therapy (PDT) for actinic keratoses (AK), Bowen's disease (BD) and superficial basal cell carcinomas (BCC), and efficacy in thin nodular BCC, while confirming the superiority of cosmetic outcome over standard therapies. Long term follow-up studies are also now available, indicating PDT has recurrence rates that can be superior to cryotherapy in AK (depending on protocol), equivalent to other standard therapies in BD and superficial BCC, but inferior to surgery in nodular BCC. Current evidence does not support the use of topical PDT for invasive squamous cell carcinoma. Sufficient evidence now exists for the use of PDT in epidermal dysplasias in transplant recipients, but evidence levels remain poor, despite encouraging case series and reports for PDT in vaginal intra-epithelial neoplasia and extra-mammary Paget's. PDT can reduce the number of new lesions developing in patients at high risk of skin cancer and may have a role as a preventive therapy.
The method of delivery of topical PDT is increasingly standardised with widespread approvals for the use of methyl-ALA cream in Europe, typically applied 3 hours before illumination using a red LED light source. A patch containing 5-ALA has also been studied in patients with multiple AK, with efficacy and cosmesis superior to cryotherapy and sustainability of response over 12 months. A nano-emulsion formulation of ALA is also under investigation for treating actinic keratoses. The light sources used in PDT impact on efficacy, with modern red LED devices both effective and easy to operate. Recent studies of ambulatory PDT, where a low irradiance portable LED device is worn by the patient, may further facilitate delivery of this therapy. The substitution of a light source by using daylight has shown equivalent efficacy to LED light, in clearing facial AK by MAL-PDT.
The management of treatment-related pain remains a challenge in a minority of patients, but the modality is otherwise well-tolerated. Studies concerning long term safety provide reassurance over the repeated use of PDT.
PDT offers the advantage of providing an office/hospital delivered therapy, maximizing compliance, with the potential for treating multiple lesions concurrently, with a predictable pattern of tissue reaction, and high quality cosmesis. Depth of therapeutic effect still limits its therapy range in nodular BCC, although adjunctive debulking curettage prior to treatment can achieve high clearance rates. The development of new drug formulations and light sources will hopefully simplify delivery as well as see a wider group of patients benefit from this modality.
Key Words: Actinic keratoses, Bowen's disease, basal cell carcinoma, photodynamic therapy