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Photodynamic therapy and fluorescence diagnosis of skin cancers
Rolf-Markus Szeimies1, Michael Landthaler
1Department of Dermatology, University of Regensburg, Germany.
Abstract:
In several countries throughout the world the photosensitizer porfimer-sodium has been approved for systemic photodynamic therapy (PDT) for different oncological indications. However, owing to the prolonged photosensitization entailed, the use of this porphyrin derivative is restricted. Currently, the most promising sensitizers in dermatology that can be applied topically are 5-aminolevulinic acid (ALA) or ester derivatives that are precursors of heme biosynthesis. ALA has shown good clinical and excellent cosmetic results in superficial skin cancer and precancerous conditions, e.g. superficial basal cell carcinoma (BCC), or actinic keratoses (AK): phase III studies have demonstrated its efficacy especially in Bowen's disease and AK. ALA-PDT for AK was therefore approved by the FDA in late 1999, and the corresponding registration process is currently in train in Europe. Besides its usefulness in oncological therapy, ALA also has a unique feature that can be exploited for diagnostic purposes: after topical or systemic application protoporphyrin IX is induced rather selectively in epithelial tumors, with a high tumor-to-surrounding tissue ratio, which can be visualized after excitation with light. By using a CCD camera system together with digital imaging, the contrast of the acquired fluorescence images can be significantly enhanced and allows the determination of a threshold, which can be utilized either for a directed biopsy or for preoperative planning when Mohs' surgery is scheduled. At present, the routine employment of such systems is being assessed in prospective studies.
Insights
Topical 5-aminolevulinic acid (ALA) photodynamic therapy (PDT) shows promise for skin cancer treatment and diagnosis. ALA-PDT offers effective oncological therapy and improved diagnostic capabilities for epithelial tumors.
Area of Science:
- Dermatology
- Oncology
- Photodynamic Therapy
Background:
- Porphyrin-sodium photodynamic therapy (PDT) is approved but restricted due to prolonged photosensitization.
- Topical 5-aminolevulinic acid (ALA) and its derivatives are promising photosensitizers in dermatology.
- ALA is a precursor of heme biosynthesis, showing efficacy in superficial skin cancers and precancerous conditions.
Purpose of the Study:
- To evaluate the efficacy and diagnostic potential of 5-aminolevulinic acid (ALA) in photodynamic therapy (PDT).
- To explore ALA's role in treating superficial skin cancers and precancerous conditions.
- To investigate ALA's utility in tumor visualization for diagnosis and surgical planning.
Main Methods:
- Systemic and topical application of 5-aminolevulinic acid (ALA).
- Photodynamic therapy (PDT) utilizing ALA as a photosensitizer.
- Fluorescence visualization of induced protoporphyrin IX in epithelial tumors using CCD camera and digital imaging.
Main Results:
- ALA-PDT demonstrates good clinical and cosmetic results for superficial skin cancers like basal cell carcinoma and actinic keratoses.
- Phase III studies confirm ALA-PDT efficacy in Bowen's disease and actinic keratoses.
- ALA induces protoporphyrin IX selectively in epithelial tumors, enabling visualization with high tumor-to-tissue ratio for diagnostic purposes.
Conclusions:
- ALA-PDT is an effective treatment for various superficial skin cancers and precancerous conditions.
- ALA's fluorescence properties offer a valuable tool for tumor diagnosis and surgical planning.
- Further prospective studies are assessing the routine employment of ALA-based fluorescence imaging systems.