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.

This is a randomized, double-blind clinical trial, parallel, placebo-controlled trial. Breast cancer women treated surgically and with indication for adjuvant chemotherapy, aged between 18 and 75 years will be included. Patients will be randomized to receive 20mg of melatonin or placebo at bedtime. Treatment will initiate seven days before the start of chemotherapy to three days after the first cycle, totaling ten days. The sleep-wake rhythm will be assessed by actigraphy, which use will precede three days to start treatment. We will also evaluate the sleep-wake cycle by sleep diary. Other parameters will be measured as depressive symptoms, pain threshold pressure, effect on platelets and white series, the pain response to conditioned stimuli and quality of life. Serum markers of neuroplasticity will be measured as the Derivate Nerve Factor Brain BDNF and S100 β. The icronucleus effect will quantified by cell material from the oral mucosa. We expect that the use of melatonin, as a competitor to chemotherapy and synchronizer, improves tolerance to adjuvant treatment of breast cancer chemotherapy adverse effects.

Inclusion Criteria:

• Female
• Diagnosed with breast cancer
• Indicated for the adjuvant treatment for breast cancer
• Between 18 years and 75 years
• Alphabetized

Exclusion Criteria:

• Undergone chemotherapy or radiotherapy before inclusion in the study.
• Pregnant
• Epilepsy
• Brain Stroke
• Multiple sclerosis
• BMI above 45 kg / m 2