Metformin for the Treatment of Insulin Resistance in Women With Stage I-III Breast Cancer Completing Chemotherapy

PRIMARY OBJECTIVE: I. To determine if extended release metformin hydrochloride (metformin) can normalize glycosylated hemoglobin (HgbA1c) (\< 5.7%) for women breast cancer survivors with HgbA1c between 5.7-6.4%. EXPLORATORY OBJECTIVES: I. To investigate whether metformin treatment of insulin resistance (versus standard of care alone) alters epigenetic changes (chromatin acetylation, chromatin opening, and methylation) and the level of inflammatory cytokines. (Pilot) II. To investigate whether normalization of HgbA1c alters epigenetic changes (chromatin acetylation, chromatin opening, and methylation) and the level of inflammatory cytokines. (Pilot) OUTLINE: Patients are randomized to 1 of 2 arms. ARM I: Patients receive standard of care healthy diet and exercise handouts and extended release metformin orally (PO) once daily (QD) for 12 months in the absence of disease progression or unacceptable toxicity. Additionally, patients undergo blood sample collection throughout the study. ARM II: Patients receive standard of care healthy diet and exercise handouts on study. Additionally, patients undergo blood sample collection throughout the study. After completion of study treatment, patients are followed up at 30 days and in 12 months.