Photodynamic therapy for skin cancer can cause immense burning pain to patients.
Researchers recently discovered the reason why photodynamic therapy for early-stage skin cancer causes severe pain for patients.
Photodynamic therapy can cause similar paleness and photosensitivity as porphyrias, which is a metabolic disorder that affects haem in the blood.
This treatment uses a cream that stimulates haem production in cancer cells, and produces prophyrins that create aggressive free oxygen radicals when exposed to light, according to a study published in the Journal of Neuroscience. When cancer cells are exposed to the free oxygen radicals, they die.
Researchers in the study used patients whose skin was exposed to a dark blue laser pointer that has the right wavelength to promote the production of free oxygen radicals. The patients felt prick-like pain when they were exposed to the light for 30 seconds.
Researchers also found that patients who used the cream beforehand experienced much stronger pain, and could not stand exposure to the laser beam for more than 40 seconds, according to the study. When exposed to red light, which has a longer wavelength, patients treated with the skin cream also felt burning pain.
The researchers found that free oxygen radicals were active in both the diseased cells and nerve endings that activate TRPA1, the ion channel that triggers pain or itching. Additionally, the cream activated TRPV1, which triggers burning sensations.
The activation of these ion channels are known to cause pain and inflammation, according to the study.
“Medications that block both ion channels have already been tested in the treatment of other types of pain, such as the pain experienced in diabetic neuropathy or arthritis,” concluded researcher Peter Reeh, MD, PhD. “Based on the findings of this study, these should have two benefits in this case, as they would reduce both pain and inflammation.”