Use of Metformin to Reduce Cardiac Toxicity in Breast Cancer

Inclusion Criteria: * Breast cancer requiring neoadjuvant or adjuvant therapy with doxorubicin * Complete metabolic panel demonstrating adequate organ functions as defined by the following: Aspartate transaminase (AST) less than 2.5 times Upper Limit of Normal (ULN); Alanine transaminase (ALT) less than 2.5 times ULN; alkaline phosphatase less than 2.5 times ULN; serum creatinine less than 1.5 mg/dL; serum bilirubin less than ULN * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 * Age greater than or equal to 21 years Exclusion Criteria: * Known diabetes * History of cardiac arrhythmias or symptomatic cardiac disease * Currently taking antiarrhythmic medications, beta-blockers, or other rate controlling cardiac medications * Currently taking metformin and/or sulfonylureas * Known hypersensitivity or intolerance to metformin * Baseline ejection fraction of less than 50% measured by echocardiogram * Known hypersensitivity to contrast used during echocardiogram * Risk factors associated with increased risk of metformin-associated lactic acidosis (e.g. congestive heard failure, history of acidosis, habitual intake of 3 or more alcoholic beverages per day) * Pregnant or breast feeding