INTRODUCTION: Radiotherapy (RT) is an essential cancer treatment and is estimated that approximately 52% of oncological patients will be submitted to this technique once. However, some tumors, such as triple-negative breast cancer (TNBC), present radioresistance, demanding high doses of ionizing radiation (IR) and a prolonged period of treatment, which contributes to secondary malignancies due to deposition of dose in organs at risk and several side effects. Moreover, this subtype of cancer shows a high incidence of metastasis and decreases the survival expectancy of the patient. Thus, the search for new agents that can act as a radiosensitizer to improve the RT effects has been growing. Conversely, photobiomodulation therapy (PBM), which is a promising therapy with increasing adhesion in clinical practice, has been used to mitigate the adverse effects of RT. Indeed, recent studies have associated PBM with RT to combat cancer. OBJECTIVES: In this study, we used TNBC-bearing mice as a radioresistant cancer model to verify if PBM could act as a radiosensitizer MATERIALS AND METHODS: PBM was applied in two different protocols before the RT with a high dose (60 Gy fractioned in 4 sessions). We evaluated the tumor volume progression, animal clinical evolution, lung metastases by optical coherence tomography, and animal survival DISCUSSION AND RESULTS: Our data indicate that PBM before each RT session arrested the tumor volume, improved the clinical signals of the animals, reduced the nodules in the lung, and extended animal survival. CONCLUSION: In the light of the knowledge gained, our data indicate that PBM could act as a radiosensitizer.