Can Photodynamic Therapy Shine a Brighter Light on Dermatological Treatment?

🔍 Key Finding Topical PDT is effective for a widening range of oncological, infectious, and inflammatory skin conditions, and new methods of delivery, including daylight and artificial daylight PDT, are increasing treatment options and enhancing efficacy. Potential biomarkers, such as Myc and PTEN, may help predict responsiveness to PDT.

🔬 Methodology Overview

• Design: Review of presentations and posters from the 2022 European Society for Photodynamic Therapy (Euro-PDT) Annual Congress.
• Data Sources: Presentations and posters from the Euro-PDT 2022 congress.
• Selection Criteria: Focus on advances in research and clinical applications of PDT in dermatology.
• Analysis Approach: Qualitative synthesis of findings presented at the congress, supplemented by relevant literature references.
• Scope: Broad overview of PDT applications, including non-melanoma skin cancer, acne, photoaging, and other emerging indications. Also covers advances in PDT delivery methods and combination therapies.

📊 Results

• Daylight PDT (dPDT) Dose Model Validation: A global validation study confirmed the accuracy of a model for determining dPDT dose using inexpensive luxmeters, with a median deviation of ±10% and a maximum deviation of ±20% from gold-standard spectral irradiance measurements.
• Real-world dPDT Effectiveness: Hospital-initiated dPDT achieved clearance or good response in 61% of 186 patient treatment courses for actinic keratoses (AK), with 83% of patients preferring dPDT over other AK therapies. Home-based dPDT showed similar efficacy (66%).
• Calcitriol Enhanced dPDT: Pre-treatment with calcitriol before MAL-dPDT for AK on the upper extremities showed slightly higher response rates (64.04% vs. 57.93%) and a significantly higher response rate for grade II/III AKs (55.24% vs. 39.58%), but also increased local skin reactions.
• Biomarkers for dPDT Response: Overexpression of the Myc proto-oncogene and underexpression of the PTEN tumor suppressor gene were associated with poor response to dPDT in patients with field cancerization and AK.
• PDT for BCC Subtype Diagnosis: Clinical diagnosis of superficial basal cell carcinoma (BCC) suitable for PDT was reliable in 93% of cases, but clinical diagnosis of nodular BCC had only 54% specificity, highlighting the need for pre-PDT biopsy, especially for suspected nodular lesions.
• PDT for Acne: A split-face study showed that two or four treatments of MAL PDT resulted in a 74% and 85% relative decrease in inflammatory acne lesions, respectively, at 20 weeks. Adverse events were generally mild.
• PDT for Uncommon Conditions: Case reports and small series presented at the conference demonstrated successful PDT treatment of various uncommon conditions, including cutaneous alternariosis, pseudolymphoma, acral resistant warts, eyelid Bowen’s disease, and Mycobacterium marinum infection.

💡 Clinical Impact This review highlights the expanding role of PDT in treating various dermatological conditions, including uncommon conditions like tinea capitis and cutaneous alternariosis, and emphasizes the increasing choice in PDT delivery methods, such as daylight and artificial daylight PDT, as well as wearable light-emitting fabrics. This wider choice, combined with opportunities to enhance efficacy through combination therapies, expands treatment options and personalizes care for patients.

🤔 Limitations

• PDT should be avoided as a routine therapy for invasive squamous cell carcinoma.
• Scientific proof for combination therapies remains limited due to variations in study design, endpoints, and baseline PDT efficacy.
• The actual number of cleared lesions does not indicate a reduction in the risk of SCC. Non-responding lesions may carry a greater risk.
• Clinical diagnosis alone may not be sufficient for assessing BCC suitability for PDT, particularly for nodular lesions; pre-PDT biopsy is recommended.
• PDT for melanoma faces challenges such as resistance mechanisms (melanosomal trapping, melanin pigment).
• For some non-neoplastic conditions (necrobiosis lipoidica, psoriasis, rosacea), there is poor quality evidence to support PDT use.
• More adverse events are to be expected with laser-assisted drug delivery, including greater pain, possible need for prophylaxis, and stricter photoprotection. Careful parameter setting is crucial.
• Realistic expectations are needed for aesthetic PDT, even with intensified protocols. Deep wrinkles and sebaceous hyperplasia may show only mild improvement.

✨ What It Means For You Dermatologists should consider PDT for a wider range of oncological, infectious, and inflammatory skin conditions, including acne and photoaging, utilizing various delivery methods like conventional, daylight, and artificial daylight PDT. Emerging technologies like light-emitting fabrics and combination therapies offer enhanced treatment options, but clinicians should be mindful of potential increased side effects and the need for personalized treatment plans based on individual patient factors and biomarkers.

Reference Morton CA, Szeimies R-M, Braathen LR. Review of the European Society for Photodynamic Therapy (Euro-PDT) Annual Congress 2022. Eur J Dermatol. 2023;33:467-473. https://doi.org/10.1684/ejd.2023.4562