PRESCOTT, Ariz. -- Firefighters "fight fire with fire" to stop spreading. Dermatologists have a similar technique - they "sunburn" patients to prevent precancerous skin lesions called actinic keratoses.
"Actinic keratoses are caused by sun exposure and they are the precursor to skin cancer," said Dr. Charles Johnson of Arizona Dermatological Group in Prescott. "Actinic keratoses can appear as red or brown spots or yellow discoloration. They are crusty or flaky areas on the skin usually found on the face and scalp."
Johnson's office recently started treating patients using Levulan Photodynamic Therapy. PDT therapy combines applying a topical solution to skin and "burning" it with blue light exposure.
Levulan PDT kills the actinic keratoses that could evolve into cancerous squamous cells, he said.
"The Levulan PDT treatment kills the visible AKs in the same way that freezing or lasing kills them," he said. "But the beauty of PDT is that it also kills the cancerous cells that you can't see.
"That is what makes this such a great preventative treatment for skin cancer."
Photodynamic therapy is a two-step procedure.
The first step involves thoroughly cleaning the patient's skin and spreading on Levulan topical solution. The Levulan "incubates" from one to five hours.
"The longer the incubation, the deeper the Levulan solution penetrates," Johnson said. "The photo-damaged cells absorb the Levulan, which is converted to light-sensitive porphyrins. Porphyrins are naturally produced chemicals in cells. The porphyrins react to the blue light and damage the cells that then die. Healthy cells are not affected.
"It is just like getting a sunburn."
Before going into the blue light, Johnson places eye patches over the patient's eyes. The patient's head goes inside a semicircular bank of tube lights for 16 minutes and 40 seconds, or 1,000 seconds total.
The sensation and level of discomfort during the light treatment varies from patient to patient, Johnson said.
"I've had one patient who quit after eight seconds, and others who have sat through the entire time without any complaint," he said. "The level of burn depends on the amount of unseen photo damage."
One patient told Johnson that it "felt like his face was on fire."
Johnson provides a hand-held fan and squirt bottle with water to cool the skin during the light exposure.
Post-treatment of PDT therapy is similar to treating sunburn.
"The Levulan stays active for 24 hours after it is applied, so we tell patients to stay out of the sun and put on sunscreen if they are going outdoors," Johnson said.
"Receiving the treatment does not mean you never have to use sunscreen again," said Ronnie Cameron, clinical supervisor. "If you lose a bunch of weight and start overeating again you will gain the weight back. If you go back out in the sun without protection you will get more actinic keratoses."