This study is looking at whether Metformin, an agent that is commonly used to treat diabetes, can decrease or affect the ability of breast cancer cells to grow and whether Metformin will work with other therapies to keep cancer from recurring. Health Canada has not approved the sale or use of Metformin to treat breast cancer, although they have approved its use in this clinical trial. Although Metformin is approved by the FDA for the treatment of diabetes, its use in breast cancer is considered investigational.