Breast cancer is the second most common cancer in the world, the most common in women, representing the leading cause of death in Brazil. The therapeutic approach for breast cancer includes surgery, radiotherapy, chemotherapy and endocrine therapy. Chemotherapy courses with side effects because the cytotoxic effects affect indistinctly neoplastic cells and normal cells. The cancer per se may promote disruption in circadian rhythm. Chemotherapy induces or enhances desynchronization of the sleep-wake cycle, which competes with impaired memory, mood, pain and poor quality of life. Melatonin is an attractive therapeutic option in this context. This neurohormone also has immunomodulatory, co-analgesic and anti-depressant properties. Additionally, the antioxidant properties of melatonin may decrease free radical formation, reducing damage to DNA. The objective is to assess the response to melatonin as a synchronizer of the sleep-wake rhythm, neuromodulator, and mieloprotetor genoprotetor in the effects induced by chemotherapy in women with breast cancer.