Methyl Aminolevulinate-PDT for Actinic Keratoses and Superficial Nonmelanoma Skin Cancers

B. Ortiz-Policarpio, MD; H. Lui, MD, FRCPC

Disclosures

Skin Therapy Letter. 2009;14(6) 

In This Article

Abstract

Methyl aminolevulinate-hydrochloride cream (Metvix® [in Canada] and Metvixia® [in the US], Galderma) in combination with photodynamic therapy (PDT) provides an effective treatment option for actinic keratoses (AKs), superficial basal cell carcinoma (sBCC), and Bowen's disease (BD). Good clinical outcomes have been reported in the literature. Complete responses (CRs) in AK range from 69% to 93% at 3 months. In sBCC, reported CR rates were from 85% to 93% at 3 months and almost on par with cryosurgery at 60 months (75% vs. 74%). In BD, CR rates were 93% at 3 months and 68% at 2 years. Current evidence has shown that this noninvasive treatment is superior in terms of cosmetic outcome to other management strategies such as surgery. It also offers the advantages of relative simplicity, low risk of side-effects and decreased complications due to scar formation.

Topical Methyl Aminolevulinate (MAL)-PDT

Photodynamic therapy (PDT) treats superficial skin cancers and pre-cancerous lesions through photosensitized reactions requiring oxygen. Over the past several decades, PDT has been extensively investigated as an experimental therapy for human cancers. There is now growing interest in the use of PDT not only for nonmelanoma skin cancer (NMSC), but also for other skin tumors such as lymphoma, as well as for nononcological indications, such as psoriasis, localized scleroderma, acne, and skin rejuvenation.[1,2,3,4] In Europe, as well as in the US, porphyrin-inducing precursors, such as 5-aminolevulinic-acid (ALA) and MAL have been proven effective for the treatment of actinic keratoses (AKs) and basal cell carcinomas.[5,6,7] Both ALA and MAL induce protoporphyrin IX (PpIX) locally in the skin. Photodynamic therapy combines the simultaneous presence of a photosensitizer activated by an appropriate wavelength of light. For topical PDT, upon illumination, PpIX is transformed to the excited state and then returns to its ground state through a type-II photo-oxidative reaction.5 In this reaction, these molecules transfer energy to oxygen producing highly reactive oxygen species (ROS), singlet oxygen in particular. ROS accumulates locally within the affected tissue leading to direct cellular damage by apoptosis or necrosis, and indirect stimulation of inflammatory cell mediators.[6]

Previous studies have shown that MAL in combination with red light (570-670nm) has provided good clinical outcomes in the treatment of NMSC (both sBCC and Bowen's disease) and AKs.[7] MAL, the methylated ester of ALA, is a new topical photosensitizer that may offer advantages over ALA in terms of its deeper skin penetration (up to 2mm in depth) due to potentially enhanced lipophilicity and greater specificity for neoplastic cells.[8] In a typical PDT session, the lesion surface is prepared by light curettage of any surface crusts and scales. The 3 hour application of 160mg/g MAL prior to irradiation with 37J/cm2 from a light-emitting diode system (emission peak of 632nm) corresponds to the time point of the highest ratio of fluorescence depth to tumor depth2 under occlusion. Two treatments 1 week apart for AKs, sBCC, and BD have been recommended; however, a single treatment session is possible and may be potentially sufficient for very thin AKs. For partially cleared responses, a second treatment course (consisting of two weekly PDT sessions) at 3 months may be considered.[9] This article reviews key published trials of topical MAL-PDT for AK, sBCC, and BD.

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