• Primary outcome: To compare the patient complete response rate of MAL PDT to that of vehicle PDT 3 months after the last treatment in patients with multiple actinic keratoses on the face and/or scalp
  

• The secondary outcomes: To compare local Adverse Events (treatment site Adverse Events (AEs) between MAL PDT and vehicle PDT; To compare the lesion complete response rate between MAL PDT and vehicle PDT 3 months after last treatment
  

Actinic keratoses are pre-malignant skin lesions, which may develop to squamous cell carcinomas (SCC). They are usually small, thin, erythematous, de-squamating lesions on light exposed atrophic skin and the lesions are often multiple.

Photodynamic therapy (PDT) is the selective destruction of abnormal cells through light activation of a photosensitiser in the presence of oxygen. These cells accumulate more photosensitiser than normal cells. The photosensitiser generates reactive oxygen species upon illumination.

For skin diseases, such as actinic keratosis (AK), there has been an increasing interest in using topically applied precursors of the photoactive porphyrins (PAP). The most commonly used precursors have been 5-aminolevulinic acid (ALA) and its derivatives. The present test drug contains methyl aminolevulinate, which penetrates the lesions well and shows high lesion selectivity.

Different light sources (i.e. CureLight, Aktilite CL16 and Aktilite CL128) have been used for the activation of PAP, which absorbs light in the range of 400-700 nm. The present study uses the Aktilite CL 128 lamp. Aktilite 128 is based on LED technology and emits a narrow red light spectrum with an average wavelength of 630 (+/-5) nm. This study is similar to two other studies performed, on which the U.S. approval of Metvixia® cream is based except for the light source used. This study is one of two studies performed to document the safety and efficacy of the Aktilite CL 128 lamp when used in combination with Metvixia® cream.

Previous studies have shown that the risks attributed to Metvixia® PDT are few and related mainly to transient pain and local erythema during and shortly after treatment. These reactions are part of the expected local phototoxicity reaction. PDT offers an advantage to other treatment modalities for actinic keratosis, being a non-invasive treatment available on an outpatient basis. Several separate lesions can be treated simultaneously and the same lesion(s) can be treated repeatedly with success. There are no known systemic toxicity or interaction with other medication. The treatment is also lesion selective, leaving the surrounding tissue intact and functional, also allowing excellent cosmetic results after treatment.