Multiple large-surface photodynamic therapy sessions with topical or systemic aminolevulinic acid and blue light in UV-exposed hairless mice.

BACKGROUND: The use of photodynamic therapy (PDT) with topical aminolevulinic acid (ALA) on large skin surfaces has recently been reported for patients with multiple actinic keratoses.

OBJECTIVE: The current study compared the ability of topical and systemic ALA-PDT as well as topical ALA-PDT with blue light to delay the appearance of UV-induced skin cancer using the hairless mouse as a model.

METHODS: Groups of hairless mice were exposed daily to UV radiation and weekly to ALA-PDT. Tumor-free survival was compared for mice exposed to UV and treated weekly with ALA-PDT and mice exposed only to UV radiation.

RESULTS: Weekly topical or systemic ALA-PDT was able to delay the induction of skin tumors. A significant difference in tumor-free survival was also observed for both actinic keratoses and invasive squamous cell carcinoma in mice treated weekly with topical ALA-PDT performed with blue light. This was observed even when weekly ALA-PDT was started after 8 weeks of UV exposure.

CONCLUSION: Large-surface topical ALA-PDT with blue light can delay the appearance of UV-induced actinic keratoses and squamous cell carcinoma in hairless mice.