Photodynamic therapy with 5-aminolaevulinic acid, dimethylsulfoxide and curettage in basal cell carcinoma: a 6-year clinical and histological follow-up

New, simplified versus standard photodynamic therapy (PDT) regimen for superficial and nodular basal cell carcinoma (BCC): A single-blind, non-inferiority, randomised controlled multicentre study

BACKGROUND

Topical photodynamic therapy (PDT) is an approved and widely used treatment for low-risk basal cell carcinoma (BCC), comprising two sessions with an interval of 1 week. Simplification of the treatment course can be cost-effective, easier to organize, and cause less discomfort for the patients.

METHODS AND FINDINGS

We performed an investigator-initiated, single-blind, non-inferiority, randomized controlled multicentre study with the objective of investigating whether a simpler and more flexible PDT regimen was not >10% less effective than the standard double PDT in the treatment of primary, superficial, and nodular ≤2 mm-thick BCC and evaluate the cosmetic outcome. With a non-inferiority margin of 0.1 and an expected probability complete response of 0.85, 190 tumours were required in each group. Histologically verified BCCs from seven centres in Norway were randomly assigned (1:1) to either receive a new regimen of single PDT with one possible re-treatment of non-complete responding tumours, or the standard regimen. The primary endpoint was the number of tumours with complete response or treatment failure at 36 months of follow-up, assessed by investigators blinded to the treatment regimen. Intention-to-treat and per-protocol analyses were performed. The cosmetic outcome was recorded. The study was registered with ClinicalTrials.gov, NCT-01482104, and EudraCT, 2011-004797-28. A total of 402 BCCs in 246 patients were included; 209 tumours assigned to the new and 193 to the standard regimen. After 36 months, there were 61 treatment failures with the new and 34 failures with the standard regimen. Complete response rate was 69.5% in the new and 81.1% in the standard treatment group. The difference was 11.6% (upper 97.5% CI 20.3), i.e. > than the non-inferiority margin of 10%. Cosmetic outcomes were excellent or good in 92% and 89% following the new and standard regimens, respectively.

CONCLUSIONS

Single PDT with possible re-treatment of primary, superficial, and nodular ≤ 2-mm-thick BCC was significantly less effective than the approved standard double treatment. The cosmetic outcome was favorable and comparable between the two treatment groups.

Expression of β-Catenin, E-Cadherin, and α-Smooth Muscle Actin in Basal Cell Carcinoma Before Photodynamic Therapy in Non-recurrent and Recurrent Tumors: Exploring the Ability of Predicting Photodynamic Therapy Outcome

Photodynamic therapy (PDT) is an effective and cosmetically beneficial treatment of low-risk basal cell carcinomas (BCCs). To optimize PDT response, it is important to correctly select tumors. We sought to find markers that could identify such tumors beyond contributions from clinical and histological examination. Studies have shown that β-catenin, E-cadherin, and α-smooth muscle actin (SMA) expression can indicate BCC aggressiveness/BCC invasiveness. We wanted to use these markers in an explorative study to investigate whether they were differently expressed among non-recurring compared with recurring BCCs, to evaluate their ability of predicting PDT outcome. Fifty-two BCCs were stained with antibodies against β-catenin, E-cadherin, and α-SMA, and evaluated using immunoreactive score (IRS), subcellular localization, and stromal protein expression. Results showed that IRS of E-cadherin was significantly different among recurring compared with non-recurring BCCs and with area under a receiver operating characteristic curve of 0.71 (95% confidence interval: 0.56-0.86, p=0.025). Stromal β-catenin expression significantly increased among recurring BCCs. Some recurring BCCs had intense expression in the deep invading tumor edge. In conclusion, E-cadherin, and stromal and deep edge β-catenin expression were most prominent in BCCs that recurred post-PDT, suggesting they could potentially predict PDT outcome. Further studies are needed to investigate whether these results are of clinical value.

Acitretin Enhances the Cytotoxic Effect of 5-aminolevulinic Acid Photodynamic Therapy on Squamous Cell Carcinoma Cells

The efficacy of 5-aminolevulinic acid-mediated photodynamic therapy (ALA-PDT) on invasive cutaneous squamous cell carcinoma (cSCC) remains to be improved due to the limited penetration of this treatment. Previous study showed that acitretin and ALA-PDT had synergistic effect on cSCC, but whether acitretin can enhance the cytotoxic effect of ALA-PDT on cSCC is unclear.

OBJECTIVE

To investigate whether acitretin can enhance the cytotoxic effect of ALA-PDT on SCL-1 cells, as well as the possible mechanism involved.

METHODS

Inverted microscopy, trypan blue exclusion assay, and flow cytometry were used to studied the morphology, viability and apoptosis of SCL-1 cells treated with acitretin, ALA-PDT and acitretin followed by ALA-PDT treatment, respectively. Confocal microscopy was applied to detect the ROS formation of SCL-1 cells treated with acitretin of four different concentrations. The ROS formation of SCL-I cells treated with acitretin of four different concentrations followed by ALA-PDT treatment was detected using confocal microscopy and flow cytometry.

RESULTS

SCL-1 cells exhibited a significant morphological alteration when treated with acitretin followed by ALA-PDT. The combination of acitretin and ALA-PDT induced a higher cell death rate and apoptosis than that with acitretin or ALA-PDT treatment alone. ROS could be induced when incubated with acitretin at a concentration of 6.4 × 10^-4mg /mL or above. However, a higher level of ROS formation was observed when SCL-1 cells were treated with acitretin followed by ALA-PDT than that with ALA-PDT or acitretin alone.

CONCLUSION

Acitretin can enhance the cytotoxic effect of ALA-PDT on SCL-1 cells, possibly via the ROS pathway.

Randomized trial of topical ascorbic acid in DMSO versus imiquimod for the treatment of basal cell carcinoma

Skin cancer is the most common cancer in the United States and among Caucasians worldwide, with more people diagnosed each year than all other cancers combined. Basal cell cancer is the most common form with an estimated 4.3 million cases diagnosed annually, and treatment costs estimated at $4.8 billion. The objective of this study was to compare efficacy of a topical solution consisting of 30% ascorbic acid in 95% dimethylsulfoxide with topical imiquimod in the treatment of basal cell carcinoma. Twenty-five patients with 29 biopsy confirmed basal cell carcinomas were randomly assigned to receive either the topically applied ascorbic acid treatment twice daily for 8 weeks or topical imiquimod, a standard and well characterized topical treatment. After 8 weeks, post-treatment biopsy of lesions showed complete resolution of 13/15 (86.7%) in the ascorbic acid group, while 8/14 (57.1%) lesions in the IMQ group were resolved (p < 0.05 Chi Square). Topical ascorbic acid was superior at 8 weeks, and non-inferior at 12 weeks to topical imiquimod in the treatment of low risk nodular and superficial lesions. In addition, ascorbic acid was associated with fewer adverse effects than imiquimod. 70% of patients in the imiquinod group showed residual hypopigmentation at 30mo follow up versus 0% in the ascorbate group.

Non-surgical treatments for basal cell skin cancer

Basal cell carcinoma is the most common nonmelanoma skin cancer. It originates from undifferentiated cells in the basal cell layer of the epidermis or from the outer root sheath of the hair follicle. The most important factor in development of basalioma is ultraviolet radiation. Surgery is considered the gold standard of treatment for basal cell cancer. However, nonsurgical options are available for individuals who are unsuitable for surgery. The purpose of this review is to summarize the efficacy and indications of alternative, nonsurgical treatments that can be used in the management of basal cell cancer Effective nonsurgical treatments include destructive methods (eg, curettage and electrodessication, cryosurgery, laser), photodynamic therapy, topical medications, hedgehog pathway inhibitors. Nonsurgical therapeutic alternatives are safe and effective for the treatment of BCC. Factors such as tumor location, size, and histopathological subtype should be taken into consideration when selecting optimal treatment, cosmetic results and patient preference should be considered too. To search for the necessary literature, the PubMed, MedLine, Web of Science and RSCI databases were used.

Photodynamic therapy of oral lichen planus

Oral lichen planus (OLP) is a chronic inflammatory and immune-mediated disease affecting the oral mucosa. OLP presents with asymptomatic, lacelike white stripes and/or symptomatic red, ulcerated mucous membranes. Eating, drinking and oral hygiene procedures may be painful resulting in reduced quality of life (QOL). The histopathological picture is a zone of cellular infiltrate, mainly CD8+ cells, in the superficial layer of the connective tissue and signs of liquefaction degeneration of the basal membrane. Conventional treatment is corticosteroids. Local and systemic side effects are common, and patients may develop drug resistance. The intention with this article is to demonstrate the heterogeneity in photodynamic therapy (PDT) of OLP. A search in PubMed, Embase (Ovid) and Medline (Ovid) identified seventeen clinical studies investigating PDT of OLP. Only five were randomised controlled studies and the study groups varied from 5 to 50 patients. Five different photosensitisers or precursors were tested. Both broadband spectrum lamps, lasers and light-emitting-diodes (LEDs), with wavelengths from 420 nm to 682 nm, were used. The number of treatment sessions varied from one to ten. The patients were followed up for 0 to 48 months, but in thirteen studies the post treatment observation time was ≤6 months. Single arm studies demonstrated improvement of OLP except in one study. In all controlled studies except for one, PDT was superior or equal to conventional treatment. The majority of patients experienced a slight burning sensation during light activation, but no serious adverse events were reported. Only few studies examined the effect of PDT on a cellular level.

5-aminolevulinic acid photodynamic therapy enhance the effect of acitretin on squamous cell carcinoma cells: An in vitro study

Squamous cell carcinoma (SCC) remains the second most common nonmelanoma skin cancer (NMSC) worldwide. Both acitretin and 5-Aminolevulinic acid mediated photodynamic therapy (ALA-PDT) have validated effect on SCC. However, the effects of both treatmens remain limited, and there has been no report concerning the potential synergistic effect of both treatments for SCC.

OBJECTIVE

To investigate the cytotoxic effect of acitretin on SCL-1 cells, and whether ALA-PDT enhances this effect.

METHODS

CCK-8 and trypan blue exclusion array were used to detect the cell cytotoxicity after acitretin treatment with different concentrations (1.6 × 10^-4mg/mL, 1.6 × 10^-3 mg/mL, 1.6 × 10^-2mg/mL and 1.6 × 10^-1mg/mL) for 24 h, 48 h and 72 h. Flow cytometry and trypan blue exclusion assay were used to detect the apoptosis and viability of SCL-1 cells after treated with acitretin, ALA-PDT and ALA-PDT immediately followed by acitretin. Independent sample t test was used to analyze the different incubation time of acitretin and acitretin combined with ALA-PDT on SCL-1 cells. Bonferroni Test One-way Anova method was used to analyze the effect of different treatment on the SCL-1 cells.

RESULTS

A significant cytotoxic effect was observed after acitretin treatment, in an acitretin concentration-dependent manner within the range of 1.6 × 10^-4mg/mL to 1.6 × 10^-1mg/mL and an acitretin incubation time-dependent manner within 24 h-72 h. The total apoptosis rate and dead cells rate in group of ALA-PDT combined with acitretin were both significantly higher than that of acitretin, ALA-PDT group. A stronger apoptotic and cytotoxic effect detected 24 h after treated with acitretin than that of 12 h was observed in this study.

CONCLUSION

Acitretin has a cytotoxic effect on SCL-1 cells, and ALA-PDT treatment enhances the the cytotoxic effect of acitretin.

Photodynamic therapy in superficial basal cell carcinoma treatment

Basal cell cancer (BCC) is an epithelial neoplasm that arises from basal cells, which constitute the lower layer of the epidermis. Global statistics have shown the progressive increase in the incidence of skin cancer in several countries. The cumulative exposure to solar radiation (ultraviolet B) in the first two decades of life represents the critical risk for the disease. Preclinical and clinical trials have shown photodynamic therapy (PDT) as a promising innovation for treatment of skin cancers, especially to the non-melanoma group. The authors reviewed trials with photodynamic therapy in superficial basal cell carcinoma with different photosensitizers to better evaluate how PDT modifies the natural history of sBCC. We conclude trials should not assess only the immediate efficacy but the main goal of long-term effectiveness of the protocols in order to generate best evidence for clinical practice.

Nonsurgical Options for the Treatment of Basal Cell Carcinoma

Objectives

The aim of this review article is to summarize the effectiveness, potential adverse events, and indications of the main nonsurgical treatment alternatives for basal cell carcinoma.

Methods

An extensive literature review was carried out. The most relevant articles were discussed and selected by the authors in order to provide a brief but evidence-based overview of the most common nonsurgical methods used for treating basal cell carcinoma.

Results

Although surgery and Mohs micrographic surgery are often considered the optimal treatment options for basal cell carcinoma, these tumors can also be treated successfully with destructive techniques (eg, curettage alone, cryosurgery, or electrodesiccation), photodynamic therapy, topical drugs (eg, 5-fluorouracil, imiquimod, or ingenol mebutate), radiotherapy, or hedgehog pathway inhibitors. When choosing between these alternatives, physicians must take into consideration the tumor's size, location, and histopathological subtype. Special care should be taken when treating recurrent tumors. Furthermore, physician experience is of great importance when using destructive techniques. Finally, patient preference, potential adverse events, and cosmetic outcome should also be considered.

Conclusions

Dermatologists and physicians treating basal cell carcinoma should have knowledge of and experience with the large arsenal of therapeutic alternatives available for the successful, safe, and individualized management of patients with basal cell carcinoma.

Blue light versus red light for photodynamic therapy of basal cell carcinoma in patients with Gorlin syndrome: A bilaterally controlled comparison study

BACKGROUND

Photodynamic therapy (PDT) is a non-scarring alternative for treating basal cell carcinoma (BCC) in patients with Basal Cell Nevus Syndrome (BCNS), also known as Gorlin syndrome. In Europe, red light (635 nm) is the predominant source for PDT, whereas in the United States blue light (400 nm) is more widely available. The objective of this study was to conduct a head-to-head comparison of blue light and red light PDT in the same BCNS patients.

METHODS

In a pilot study of three patients with 141 BCC lesions, 5-aminolevulinate (20% solution) was applied to all tumors. After 4 h, half of the tumors were illuminated with blue light and the remainder with red light. To ensure safety while treating this many tumors simultaneously, light doses were escalated gradually. Six treatments were administered in three biweekly sessions over 4 months, with a final evaluation at 6 months. Tumor status was documented with high-resolution photographs. Persistent lesions were biopsied at 6 months.

RESULTS

Clearance rates after blue light (98%) were slightly better than after red light (93%), with blue light shown to be statistically non-inferior to red light. Eight suspicious lesions were biopsied, 5 after red light (5/5 were BCC) and 3 after blue light (1 was BCC). Blue light PDT was reportedly less painful.

CONCLUSION

Blue light and red light PDT appear to be equally safe and perhaps equally effective for treating BCC tumors in BCNS patients. Further studies to evaluate long-term clearance after blue light PDT are needed.

Photodynamic Therapy for Non-Melanoma Skin Cancers

Non-melanoma skin cancer (NMSC) is traditionally treated with surgical excision. Nonsurgical methods such as cryotherapy and topical chemotherapeutics, amongst other treatments, are other options. Actinic keratosis (AKs) are considered precancerous lesions that eventually may progress to squamous cell carcinoma (SCC). Photodynamic therapy (PDT) offers an effective treatment for AKs, and is also effective for superficial basal cell carcinoma (BCC). Nodular BCC and Bowen's disease (SCC in situ) have shown acceptable response rates with PDT, although recurrence rates are higher for these two NMSC subtypes. Methylaminolevulinate (MAL) PDT is a more effective treatment option than 5-aminolevulinic acid (ALA) PDT for nodular BCC. Several studies have shown that PDT results in superior cosmetic outcomes compared to surgical treatment. PDT is overall well-tolerated, with pain being the most common side effect.

Non-melanoma skin cancers: photodynamic therapy, cryotherapy, 5-fluorouracil, imiquimod, diclofenac, or what? Facts and controversies

Surgical modalities-excision, Mohs micrographic surgery, and electrodesiccation with curettage-are the preferred treatments for nonmelanoma skin cancer (NMSC). When used within guidelines, they have cure rates greater than 90%. Despite this, many other treatments have been studied and utilized for NMSC. We present a comprehensive review of the literature on these topical treatments. Photodynamic therapy (PDT) is administered under numerous and significantly varied regimens, and there are a wide range of cure rates reported. Even with aggressive regimens, PDT is not as effective as surgery is, and it is not a first-line therapy for NMSC. The cryotherapy regimen aggressive enough to adequately treat NMSC carries adverse effects and cosmetic outcomes poor enough to negate its usefulness. Topical 5-fluorouracil and imiquimod are efficacious and safe for the treatment of superficial basal cell carcinoma (BCC) but not other BCC subtypes or squamous cell carcinoma. They are self-administered twice daily for several weeks; therefore, patient and tumor selection are vital to ensuring adherence. There are currently insufficient data to support the use of topical diclofenac and ingenol mebutate for NMSC.

Photodynamic therapy with topical aminolevulinic acid

Photodynamic therapy (PDT) is a relatively new therapy in dermatology that uses the topical application of a porphyrin derivative to selectively destroy a cutaneous target. The action is implemented by the application of a specific light frequency. The ability of porphyrin to selectively target tumor tissue has been known since the 1960s. In the late 1970s, the underlying mechanism was defined, and Dougherty’s discovery of the first chromophore led to the production and commercialization of Photofrin^®. Many other chromophores that can act as photosensitizers have been studied since then, with aminolevulinic acid currently the most commonly used chromophore in clinical practice. PDT is simple, minimally invasive and can be administered on an outpatient basis. The efficacy of PDT has been proven for actinic keratosis, Bowen’s disease and basal cell carcinoma; another of its well-known applications is the treatment of photoaging. Indications for its use are continuously increasing, and promising results are reported for various skin diseases. In this paper we report the mechanism of action of PDT with aminolevulinic acid, the literature concerning the most common diseases treated with PDT and the subsequent level of evidence.

Spotlighting the role of photodynamic therapy in cutaneous malignancy: an update and expansion

BACKGROUND

Topical photodynamic therapy (PDT) is an option for the treatment of cutaneous malignancy.

OBJECTIVE

To present an update and expansion on a previous review of the use of PDT in the current literature in the treatment of actinic keratoses (AK), superficial and nodular basal cell carcinoma (sBCC, nBCC), squamous cell carcinoma (SCC), Bowen's disease, cutaneous T cell lymphoma (CTCL), malignant melanoma, and its use in chemoprevention.

METHODS

Extensive PubMed search January 2013.

RESULTS AND CONCLUSIONS

We find sufficient evidence to recommend the use of PDT in certain patients in the treatment of AK, Bowen's disease, sBCC, and nBCC. It is especially useful in those with contraindications to surgery, widespread areas of involvement, and large lesions. Not only can it be considered superior to other therapies as far as recovery time, tolerance, and cosmetic outcomes, but it also should be considered, when indicated, as first-line treatment in the above conditions. Investigations continue for the use of PDT in the treatment of melanoma, SCC, chemoprevention, and CTCL.

Non-invasive depth profile imaging of the stratum corneum using confocal Raman microscopy: first insights into the method

The stratum corneum is a strong barrier that must be overcome to achieve successful transdermal delivery of a pharmaceutical agent. Many strategies have been developed to enhance the permeation through this barrier. Traditionally, drug penetration through the stratum corneum is evaluated by employing tape-stripping protocols and measuring the content of the analyte. Although effective, this method cannot provide a detailed information regarding the penetration pathways. To address this issue various microscopic techniques have been employed. Raman microscopy offers the advantage of label free imaging and provides spectral information regarding the chemical integrity of the drug as well as the tissue. In this paper we present a relatively simple method to obtain XZ-Raman profiles of human stratum corneum using confocal Raman microscopy on intact full thickness skin biopsies. The spectral datasets were analysed using a spectral unmixing algorithm. The spectral information obtained, highlights the different components of the tissue and the presence of drug. We present Raman images of untreated skin and diffusion patterns for deuterated water and beta-carotene after Franz-cell diffusion experiment.

European guidelines for topical photodynamic therapy part 1: treatment delivery and current indications - actinic keratoses, Bowen's disease, basal cell carcinoma

Topical photodynamic therapy (PDT) is a widely used non-invasive treatment for certain non-melanoma skin cancers, permitting treatment of large and multiple lesions with excellent cosmesis. High efficacy is demonstrated for PDT using standardized protocols in non-hyperkeratotic actinic keratoses, Bowen's disease, superficial basal cell carcinomas (BCC) and in certain thin nodular BCC, with superiority of cosmetic outcome over conventional therapies. Recurrence rates following PDT are typically equivalent to existing therapies, although higher than surgery for nodular BCC. PDT is not recommended for invasive squamous cell carcinoma. Treatment is generally well tolerated, but tingling discomfort or pain is common during PDT. New studies identify patients most likely to experience discomfort and permit earlier adoption of pain-minimization strategies. Reduced discomfort has been observed with novel protocols including shorter photosensitizer application times and in daylight PDT for actinic keratoses.

High and sustained efficacy after two sessions of topical 5-aminolaevulinic acid photodynamic therapy for basal cell carcinoma: a prospective, clinical and histological 10-year follow-up study

BACKGROUND

Prolonged follow-up data on topical photodynamic therapy (PDT) in basal cell carcinoma (BCC) are necessary for a full evaluation of its effect and for comparison with conventional treatment methods.

OBJECTIVES

To assess 10-year long-term PDT efficacy in primary and recurrent BCC and to evaluate clinical and histopathological factors which may be associated with treatment failure.

METHODS

We performed a longitudinal study on 60 histologically verified BCCs in 44 patients treated with curettage and one or two sessions of dimethylsulphoxide (DMSO)-supported topical 5-aminolaevulinic acid (ALA)-based PDT. Treated lesions were investigated by clinical and histopathological examination at regular intervals. The main outcomes were 10-year lesion complete response rate using a time-to-event analysis, histological treatment failure and cosmesis.

RESULTS

Overall complete response rate for all lesions was 75% (95% confidence interval 64-87%); 60% after one and 87% after two treatment sessions. The response rate was 78% for primary lesions; 63% after one and 90% after two sessions. The cosmetic outcome was rated as good or excellent in 91-100% of evaluated cases. Treatment failure was documented in 15 (25%) of 60 lesions; clinical investigation identified 14 of them. All failures were noted within 3 years of treatment. Male gender, recurrent tumour and one treatment session were factors significantly associated with treatment failure. The only lesion larger than 2·0 cm relapsed.

CONCLUSIONS

Two sessions of DMSO-supported topical ALA-PDT and curettage can provide long-term effective treatment results with favourable cosmetic outcome in primary, small BCC.

Pre-treatment deep curettage can significantly reduce tumour thickness in thick Basal cell carcinoma while maintaining a favourable cosmetic outcome when used in combination with topical photodynamic therapy

Topical photodynamic therapy (PDT) has limitations in the treatment of thick skin tumours. The aim of the study was to evaluate the effect of pre-PDT deep curettage on tumour thickness in thick (≥2 mm) basal cell carcinoma (BCC). Additionally, 3-month treatment outcome and change of tumour thickness from diagnosis to treatment were investigated. At diagnosis, mean tumour thickness was 2.3 mm (range 2.0–4.0). Pre- and post-curettage biopsies were taken from each tumour prior to PDT. Of 32 verified BCCs, tumour thickness was reduced by 50% after deep curettage (P ≤ 0.001). Mean tumour thickness was also reduced from diagnosis to treatment. At 3-month followup, complete tumour response was found in 93% and the cosmetic outcome was rated excellent or good in 100% of cases. In conclusion, deep curettage significantly reduces BCC thickness and may with topical PDT provide a favourable clinical and cosmetic short-term outcome.

Do lasers or topicals really work for nonmelanoma skin cancers?

Novel strategies are urgently needed to address the millions of nonmelanoma skin cancers treated in the United States annually. The need is greatest for those patients who are poor surgical candidates or those prone to numerous nonmelanoma skin cancers and therefore at risk for marked disfigurement. Traditional treatment strategies include electrosurgery with curettage, radiation therapy, cryotherapy, excision, and Mohs micrographic surgery. Alternatives to traditional treatment, including topical medications and light or laser therapies, are becoming popular; however, there are various degrees of efficacy among these alternative tactics. These alternatives include topical retinoids, peels, 5-fluorouracil, imiquimod, photodynamic therapy, and lasers. The purpose of this paper is to review the available data regarding these alternative strategies and permit the reader to have a sense of which therapies are reasonable options for care.

Aminolevulinic Acid (ALA) as a Prodrug in Photodynamic Therapy of Cancer

Aminolevulinic acid (ALA) is an endogenous metabolite normally formed in the mitochondria from succinyl-CoA and glycine. Conjugation of eight ALA molecules yields protoporphyrin IX (PpIX) and finally leads to formation of heme. Conversion of PpIX to its downstream substrates requires the activity of a rate-limiting enzyme ferrochelatase. When ALA is administered externally the abundantly produced PpIX cannot be quickly converted to its final product - heme by ferrochelatase and therefore accumulates within cells. Since PpIX is a potent photosensitizer this metabolic pathway can be exploited in photodynamic therapy (PDT). This is an already approved therapeutic strategy making ALA one of the most successful prodrugs used in cancer treatment.

Guidelines for practical use of MAL-PDT in non-melanoma skin cancer

Methyl aminolaevulinate photodynamic therapy is increasingly practiced in the treatment of actinic keratoses, Bowen's disease and basal cell carcinomas. This method is particularly suitable for treating multiple lesions, field cancerization and lesions in areas where a good cosmetic outcome is of importance. Good treatment routines will contribute to a favourable result. The Norwegian photodynamic therapy (PDT) group consists of medical specialists with long and extensive PDT experience. With support in the literature, this group presents guidelines for the practical use of topical PDT in non-melanoma skin cancer.