The question comes up about once a month: can red light therapy cause cancer? “Someone told me about light therapy spreading cancer. It does not cause but could spread bad cells? I want to hear more about this. It is a pity if this is true.”
After reviewing the 192 results on pubmed.gov for (PHOTOBIOMODULATION) and (CANCER), the answer is: PBM probably does not cause cancer except possibly in high irradiation; it definitely inhibits cancer; and it has significantly helpful effects on reducing the side effects of cancer treatments.
Dr. Hamblin reviewed the literature in 2018. He concluded that PBM alleviated cancer therapy side effects and has been shown to reduce tumors rather than promote cell proliferation:
https://pubmed.ncbi.nlm.nih.gov/29466089/
There are more studies on using PBM on oral mucositis than on any other cancer therapy side effect (these are just some of the many I found):
https://pubmed.ncbi.nlm.nih.gov/34230010/
https://pubmed.ncbi.nlm.nih.gov/34021422/
and acute radio dermatitis:
https://pubmed.ncbi.nlm.nih.gov/33711412/
and dysphagia, and osteoradionecrosis:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7736953/
There are studies showing good effects on other cancer therapy side effects, such as peripheral neuropathy:
https://pubmed.ncbi.nlm.nih.gov/27887804/
And, in fact, PBM can inhibit cancer cell proliferation.
https://pubmed.ncbi.nlm.nih.gov/34182186/
https://pubmed.ncbi.nlm.nih.gov/34029847/
https://pubmed.ncbi.nlm.nih.gov/33517481/
and possibly treat oral cancer:
https://pubmed.ncbi.nlm.nih.gov/33572840/
However, meta analyses of journal articles on the use of PBM on cancer patients have mixed results.
Sometimes
PBM reduces cancer, sometimes PBM increases cancer:
https://pubmed.ncbi.nlm.nih.gov/33926421/
https://pubmed.ncbi.nlm.nih.gov/33107198/
Sometimes, it proliferates cancer in vitro, but the same dose inhibits cancer in vivo:
https://pubmed.ncbi.nlm.nih.gov/27475897/
Blue light can inhibit melanoma proliferation better at low than high irradiance, perhaps because higher irradiance produces more ROS:
https://pubmed.ncbi.nlm.nih.gov/32010497/
Whereas more ROS is preferred in killing other cancers:
https://pubmed.ncbi.nlm.nih.gov/31842333/
In fact, when testing low versus high irradiance effect upon cervical cancer cell death, irradiance of less than 0.5 J was more successful than some higher irradiances at killing cancer cell.s
Pre-cancer PBM can lead to significantly better outcomes:
https://pubmed.ncbi.nlm.nih.gov/31834561/
While PBM can contribute to therapy side effect reduction, it doesn’t, when applied for that purpose, have an effect on survival:
https://pubmed.ncbi.nlm.nih.gov/31502227/
But when PBM is applied to the same areas in a manner designed to address the cancer, and not the cancer side effects, the large irradiance treatment did have a significant effect in reducing the cancer (Petri dish only, however):
https://pubmed.ncbi.nlm.nih.gov/31479916/
Does the use of PBM against cancer or cancer therapy side effects cause cancer proliferation?
PBM does not induce tumor cell proliferation:
https://pubmed.ncbi.nlm.nih.gov/31109692/
PBM can induce tumor cell proliferation:
https://pubmed.ncbi.nlm.nih.gov/31209588/
In low irradiance, PBM does not excite tumor growth, but in high irradiance (over 9J, so not that high), it PBM does promote tumor growth: