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PDT with daylight effective in clearing AKs of the face, scalp
Photodynamic therapy using daylight was as effective as PDT with an artificial light source in clearing grade I actinic keratoses of the face and...
LAS VEGAS – The addition of field treatment to targeted lesion treatment may offer patients the best outcomes when addressing actinic keratoses (AKs), said Dr. David M. Pariser, professor of dermatology at Eastern Virginia Medical School, Norfolk, Virginia.
Speaking at the Skin Disease Education Foundation’s annual Las Vegas dermatology seminar, Dr. Pariser said that the rationale for treating AKs stems from the fact that not all AKs will transform to squamous cell carcinoma (SCC). “We don’t know which ones will and which ones won’t.” Though treatment can be guided by a shared decision-making approach, a personal history of multiple skin cancers is an obvious reason for concern, as is any drug-related or disease-related immunosuppression, he added.
Dr. David M. Pariser
Available treatments for AKs include cryosurgery, curettage, and electrodessication; photodynamic therapy (PDT); and topical agents, including 5-fluorouracil (5-FU), diclofenac, imiquimod, and ingenol mebutate.
“Cryosurgery is what most of us do for most AKs,” said Dr. Pariser, observing that this is a bread-and-butter procedure that is part of the backbone of most dermatology practices. Cryosurgery, curettage, and electrodessication are all used to treat discrete lesions, especially for higher-grade AKs.
However, Dr. Pariser noted that many AKs occur in a “field of cancerization.” This is a larger area of photodamaged skin; the skin may not appear grossly abnormal, but deranged areas will be diffusely evident with fluorescence detection, “indicating that all of this area was damaged,” he said.
PDT and topical agents effectively provide field treatment, and do not just address discrete lesions, although field treatment is technically an off-label use for these modalities, he added.
Lower concentrations and shorter courses of topical agents may be effective and better tolerated by patients, Dr. Pariser said. In clinical trials, for example, the efficacy of imiquimod 2.5% and 3.75% has been comparable to the stronger 5% formulation. Treatment cycles lasting 2 rather than 3 weeks have also shown similar efficacy. The greater palatability of these regimens to patients may increase real-world adherence as well.
Cure rates for PDT range from 67% to 92% for both the blue light–aminolevulinic acid modality and the red light–methyl aminolevulinate more commonly used in Europe. These modalities also treat a broad field, offer cure rates comparable to other topical modalities, and result in less scarring than destructive modalities, Dr. Pariser said.
The pain of PDT may be understandably off-putting for some patients, he commented. In the United States, investigators are experimenting with shorter incubation times for the ALA topical solutions. One study found comparable reductions in the number of AKs by the end of the study period for 1 versus 2 or 3 hours of incubation, and a 2-hour incubation period with spot treatment only was also similarly effective. Clearance rates ranged from about 70%-80%, and all were highly statistically significant, compared with the vehicle-only arm. However, “a second treatment at week 8 seems to be necessary for improved efficacy,” Dr. Pariser said.
Another treatment strategy currently being investigated is “painless PDT,” where the agent is applied and the field is illuminated immediately. Photo-bleaching degrades the protoporphyrins as they are produced, dramatically reducing patient discomfort. Efficacy is promising, he added.
In Europe, “daylight PDT” is being explored – the photosensitizing agent is applied, and the patient simply goes about his or her daily business in normal daylight. This is a nearly painless therapy and shows promise for efficacy. However, said Dr. Pariser, the realities of practice economics make it very unlikely that daylight PDT will catch on in the United States, since the daylight exposure does not represent a billable procedure.
Dr. Pariser reiterated that regardless of the modality, “field therapy has better long-term efficacy rates and better sustained clearance no matter which one of the agents we use, and combination therapy [of lesional and field treatment] seems to be the most effective.”
Dr. Pariser disclosed that he is an investigator and consultant for DUSA Pharmaceuticals, Photocure, and LEO Pharma, and that he discussed off-label uses of drugs and devices.
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