Effects of low level laser therapy in cancer cells—a systematic review of the literature

The aim of the present study was to conduct a systematic review regarding the use of photobiomodulation (PBM) therapy in tumoral cells, addressing the different types of lasers and parameters used. An electronic search was performed in PubMed/MEDLINE, Cochrane Library, and EMBASE databases. The inclusion criteria were being an in vitro study, with tumoral cells, and have at least one group of treatment with low-power laser and a control group (without treatment). Were excluded studies that used only non-carcinogenic cells, in vivo studies, studies that used high-power laser or the association with photosensitizers. The primary outcome evaluated was the cellular viability, and the secondary outcomes were the apoptosis rate and gene and inflammatory mediators' expression. Nineteen studies were identified among the lists of citations of studies that met the exclusion/inclusion criteria. There is a wide divergence regarding the wavelengths and doses used, as well as the type of laser, and each variation leads to different results, with some studies showing an increase in cell proliferation, while other studies showed a decrease. It is possible to suggest that PBM can be used in cancerous lesions in order to decrease the proliferation of these cells depending on the parameters used; however, the lack of standardization of laser irradiation protocols for in vitro investigations does not allow the establishment of ideal parameters for this purpose. Therefore, PBM should be used with caution in cancer patients until more studies are performed.