SEATTLE – While David Pariser, MD, said during a presentation at the annual Coastal Dermatology Symposium.
“My personal view is that, no matter how good other treatments are eventually going to be, we’re never going to give that up,” Dr. Pariser, professor of dermatology at Eastern Virginia Medical School, Norfolk, said at the meeting, jointly presented by the University of Louisville and Global Academy for Medical Education.
During the presentation, he emphasized that it isn’t always clear which actinic keratosis (AK) should be treated and which can be left alone, since most AKs don’t progress to squamous cell carcinoma (SCC). “We know that most squamous cell carcinomas arise near AKs, and many of them have histologic evidence” of AK/SCC continuum at the periphery, he said. Sun protection reduces the incidence of AKs and the incidence of nonmelanoma skin cancer, “so it’s a logical conclusion that treating AKs reduces the development of SCCs, but there are no data to show that.”
Generally, treatment decisions are made based on the presence of symptoms, location, or appearance; if the area is irritated; or there is a progressive or unusual appearance, especially if hyperkeratotic. Physician or patient concerns about cancer can prompt treatment, as should a history of multiple skin cancers or the presence of immunosuppression, he said.
Treatment options include cryosurgery, surgery, topical agents, and photodynamic therapy (PDT); Dr. Pariser focused on the latter because it is a special interest of his.
Field cancerization is based on the idea that a broad area of cells may be at risk for developing into SCC, rather than just individual AKs. Treatment with methyl 5-aminolevulinate (MAL) can reveal the extent of a problem. In some patients, “you can see a lot of fluorescence in areas that look reasonably clinically normal. So this is a piece of evidence of this field cancerization, that maybe we shouldn’t be treating individual AKs, but larger areas,” Dr. Pariser said.
With PDT, there has been some debate about how long to leave the photosensitizer on the skin before applying the light. The longer it remains, the more it spreads to nerves, which can lead to pain during the procedure. A clinical trial comparing 1-, 2-, and 3-hour wait times showed no difference in efficacy. “So 1 hour is what I do for AKs, that’s it,” Dr. Pariser said.
There are two Food and Drug Administration–approved PDT systems, a blue-light system combined with aminolevulinic acid (ALA) and a newer red-light system combined with a nanoemulsion of ALA 7.8% and a proprietary 635-nm red LED light. The nanoemulsion has the theoretical advantage in that it can penetrate more deeply into the epidermis, though this isn’t really an issue when treating AKs, according to Dr. Pariser.
A study comparing nanoemulsion of ALA, compared with a MAL cream, found the nanoemulsion to be superior in achieving complete clearance of all lesions at 12 weeks (78.2% vs. 64.2%; P less than .05). Both treatments achieved best efficacy with LED lamps, and the proprietary red light may reduce pain by allowing use of lower light intensity (Br J Dermatol. 2012 Jan; 166[1]:137-46).
Another study, Dr. Pariser said, looked at whether occlusion during drug incubation improves outcomes of blue light ALA-PDT (J Drugs Dermatol. 2012;11[12]:1483-9). Patients underwent split occlusion on the upper extremities before undergoing blue-light treatment. The median clearance rate of AKs at 8 weeks was higher with occlusion, compared with the nonoccluded areas (75% vs. 47%; P = .006), and at 12 weeks, after a second treatment (89% vs. 70%; P = .00029). There was a higher efficacy with a 3-hour incubation period, compared with studies using a 2-hour incubation period.
Application of heat can also boost success rates by increasing the synthesis of the photoactive agent, Dr. Pariser said. One study found that a simple heating pad applied to the area treated with ALA-PDT and blue light led to an 88% reduction in lesions at 8 and 24 weeks, compared with a reduction of 71% at 8 weeks and 68% at 24 weeks without heat (P less than .0001). “So if you want to give PDT a little extra oomph, add occlusion and heat,” he commented.
He also pointed out the availability of a new 4% 5-fluorouracil cream that contains peanut oil, which has similar efficacy to 5% 5-fluorouracil cream but has been associated with less pruritus, stinging/burning, edema, crusting, scaling/dryness, erosion, and erythema (J Drugs Dermatol. 2016 Oct 1;15[10]: 1218-24).
Dr. Pariser is an investigator and consultant for DUSA/Sun Pharma, Photocure, LEO Pharma, and Biofrontera. This publication and Global Academy for Medical Education are owned by the same parent company.