Investigators plan to carry out a study to investigate two different pills, Vitamin D and melatonin, and whether they can reduce the spread of cancer cells in the tumors of women with breast cancer. These pills are inexpensive and have very few side effects. A large number of studies using cell cultures and animals have shown that both vitamin D and melatonin can help destroy breast cancer cells. However thoughtful and well-designed studies are necessary on humans to see if they can decrease the spread of breast cancer, and possibly even prevent breast cancer. The proposed study aims to understand the anti-cancer activity of vitamin D and melatonin. This knowledge will assist in creating efficient cancer prevention strategies for Canadians. This study will include women with breast cancer who are being planned for surgery, and will assess whether treatment with vitamin D (dose of 2000 IU per day) in a group of 36 women, or melatonin (dose of 20mg per day) in another group of 36 women, or both pills together in yet another group of 36 women, reduces the spread of cancer cells when compared to a fourth group of 36 women who are treated with sugar pills. To do this we will measure a substance in the blood called Ki67, which provides information about the spread of cancer. Investigators will compare the Ki67 levels in the 4 groups, and all women will receive identical appearing pills so they will not know which treatment they received.

Inclusion Criteria:

• Woman with histologically confirmed invasive breast cancer (ductal, lobular, or mixed)
• Planned to undergo definitive surgery, either lumpectomy or mastectomy in 3 or more weeks

Exclusion Criteria:

• Less than 18 years of age
• Stage IIIB or IV disease
• Inoperable locally advanced or metastatic breast cancer
• Neoadjuvant chemotherapy is intended
• Currently taking vitamin D supplements
• Currently taking melatonin supplements
• Previously taking vitamin D or melatonin supplements within the last 3 months
• Currently taking a multivitamin and not willing to discontinue for the duration of the study
• Hyperparathyroid disease or other calcium disturbance in the past five years
• Active renal stones in the last six months
• Renal failure (creatinine > 190 mmol/L)
• Hypercalcemia (serum calcium > 2.6 mmol/L)
• Known pregnancy
• Participation in another clinical trial where the patient receives any other investigational product
• Unwilling or unable to provide informed consent