Safety and Clinical Impact of a Single Red Light Irradiation on Breast Tumor‐Bearing Mice

Low‐level light therapy has been used in health care as a therapeutic strategy for different diseases. However, its effects on cancer are controversial. This work evaluated the effects of three energies on breast cancer‐bearing mice after a single red light‐emitting diode (LED) irradiation. 4T1 cells were inoculated into the mammary fat pad of female BALB/c mice. When tumor volume reached 100 mm3, animals were irradiated by a LED irradiator (660 ± 11 nm) with energies of 1.2, 3.6, and 6.0 J. Control without irradiation and healthy animals were also evaluated. Mice were monitored regarding tumor volume and total blood count. After euthanasia, their organs were examined. We observed that a single irradiation does not increase tumor volume. All irradiated groups exhibited better clinical conditions than control, which presented a significant decrease in platelet and red blood cell levels compared with healthy mice. The energy of 3.6 J arrested neutrophil‐lymphocyte rate besides promoting longer survival and a lower number of metastatic nodules in the lungs. These findings suggest that a single red LED irradiation causes no impact on the course of the disease. Besides, the intermediary dose‐effect should be further investigated since it seems to promote better outcomes on breast cancer‐bearing mice. Although low‐level light therapy (LLLT) has been used to mitigate the adverse effects of cancer, its direct effects on tumors are controversial. Here, we evaluated the effects of a single red LED irradiation at three energies on breast cancer‐bearing mice. We observed that single irradiation does not increase tumor volume and causes no negative impact on the course of the disease. The middle energy arrested neutrophil‐lymphocyte rate besides promoting longer survival and a lower number of metastatic nodules in the lungs. This intermediary dose‐effect should be further investigated to help fight breast cancer.