Researchers uncover why ointment and photodynamic therapy cause pain in skin cancer patients

 Published on June 23, 2012 Apply the ointment, light on, light off - that's how easy it is to cure various forms of non-melanoma skin cancer. However, the majority of patients suffer severe pain during the so-termed photodynamic therapy. Why the treatment with ointment and red light can be so painful has now been uncovered by researchers from the RUB. They identified the ion channels involved and signalling molecules secreted by the cancer cells. "The results may provide a starting point for suppressing the pain", says Dr. Ben Novak of the Department of Animal Physiology.

How the photodynamic therapy worksIn contrast to normal cells, cancer cells are equipped with different enzymes and have a much higher metabolism. If you apply a molecule called aminolevulinic acid to the skin in the form of a gel, cancer cells take up considerably more of this substance than healthy cells. If aminolevulinic acid accumulates in the cells, the mitochondria - the power plants of the cells - form the molecule protoporphyrin IX. When irradiated with red light, protoporphyrin IX reacts with oxygen. This produces highly reactive oxygen species, free radicals, which destroy the cancer cells. Approximately ten minutes of red light irradiation is sufficient to successfully treat superficial forms of non-melanoma skin cancers such as actinic keratosis. Doctors also remove warts in this way.

Painful therapy"The catch is: it's terribly painful", says Ben Novak. Forty percent of those treated experience pain during the light irradiation, which they assess on a scale of 0 to 10 (whereby 10 corresponds to an excruciating pain like a heart attack) as 7 to 8. Using injections, like at the dentist, it is possible to numb the nerves involved. "But that also always involves a risk", says the Bochum biologist. The scientists led by the RUB professor Dr. Hermann Lübbert have now solved the mystery as to why the treatment hurts at all.