Low-level laser irradiation may stimulate proliferation of melanoma cells

Key Points

Following the final irradiation, tumors were examined regularly for 10 days.

Parallel work

Parallel work in melanoma cell cultures found no differences between the low and high doses of exposure to irradiation. This was discordant with the dose response seen in vivo. Lucio Frigo, D.D.S., Ph.D., lead author of the paper, believes this is because the culture consisted of a purified single type of cell, while a tumor in a living animal contains a diverse, complex mix of cell types that can modulate its growth.

The researchers emphasized that the high doses of irradiation used in these studies are substantially higher than those recommended by the World Association for Laser Therapy (WALT) in promoting wound healing and to treat musculoskeletal disorders.

Murad Alam, M.D., associate professor of dermatology, Northwestern University, finds the study interesting.

"It is good that someone is making an effort to obtain some empirical data on what has been posed to be a theoretical risk of using laser devices," he says. That risk has mitigated, if not eliminated, their use in the United States to treat pigmented lesions that potentially could become melanoma, he says.

Dr. Alam praises the researchers for studying in a controlled setting what would possibly be ethically challenging and expensive to study in humans.

Avoid treating melanoma

But, at the same time, Dr. Alam notes that the proof of principle study used known melanoma and irradiated those cells, causing them to proliferate.

"No clinician is suggesting that any suspected melanoma be treated with lasers of any kind, low level or higher-powered ones used in the office," he says.

Dr. Lopes-Martins agrees.

"If there is any suggestion of melanoma on the patient's skin, then avoid using laser therapy," he says. "But if we use lasers in the correct doses suggested by WALT therapy guidelines (and medical uses approved by the Food and Drug Administration), we don't see any problems."

He also believes the effect seen in his study "may be limited to local irradiation, which we applied right over the melanoma."

No cumulative effect

Dr. Lopes-Martins says there is no evidence of a cumulative effect of laser exposure on proliferation of melanoma; damage appears to be the result of the power of the laser at a single use. He is studying the dose interval between 3 and 21 J/day of exposure used in this research to better determine an upper limit for safe use.

He believes there are strong safety reasons not to use office laser equipment that generates more than 200 milliwatts of power.

Dr. Alam expects that energy levels of consumer laser products "would be very low, and the amount of time over a particular area would be too low to pose a significant risk."

He says more work remains to be done, both to confirm these findings and to determine whether LLLT can transform normal melanocytes into melanoma.