Melatonin is an attractive candidate with anticancer activities previously reported in various preclinical and clinical studies. Melatonin not only involves regulating biological rhythms and endocrine function but also functions in the occurrence, development, and treatment of cancer. There is a number of possible mechanisms by which melatonin may exert its anticancer effects. These mechanisms may include potent antioxidant, immunomodulating, oncostatic, antiproliferative, and estrogen-modulating properties. Regarding the immune-potentiating effects, melatonin increases the activity of lymphocytes, monocyte/ macrophage, and natural killer cells. Melatonin may also exert antiangiogenic and direct apoptotic effects. These activities, except for free-radical scavenging, are believed to be receptor-mediated through Melatonin-1 and Melatonin-2 receptors.

Preclinical studies have demonstrated the antitumor effects of melatonin when used alone and enhanced effects for chemotherapy when used in combination. Melatonin has shown positive results in a number of clinical trials on patients with cancer. The effect of melatonin in early stages and locally advanced breast cancer is still questioned.

Also the effect of melatonin on the development and severity of various chemotherapy-induced toxicities in breast cancer patients will be investigated.

Inclusion Criteria:

1. Confirmed diagnosis with primary invasive breast cancer.
2. Patients eligible for receiving neoadjuvant chemotherapy.
3. Eastern Cooperative Oncology Group (ECOG) performance status from 0 to 2.
4. Adequate bone marrow function (white blood count ≥4,000/mm3, platelet count≥100,000/mm3), liver function (aspartate aminotransferase and alanine aminotransferase ≤ 2.5times the upper limit of normal, serum total bilirubin < 1.5 mg/dl), renal function (creatinine < 1.5 mg/dl)

Exclusion Criteria:

1. Patients with metastatic or non-invasive disease.
2. Patients previously received chemotherapy within one month preceding randomization.
3. Patients who were previously taking melatonin.
4. Hypersensitivity to melatonin.
5. Patients with autoimmune diseases.
6. Pregnancy and lactation.