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

This phase III trial evaluates how often women develop insulin resistance and type-2 diabetes and compares metformin with usual care to usual care alone in treating insulin resistance in women with stage I-III breast cancer after chemotherapy. Insulin resistance occurs when cells stop responding to insulin and is a risk factor for developing diabetes and heart disease. Higher levels of insulin have been shown to be associated with aggressive breast cancer. Metformin hydrochloride decreases the amount of glucose (a type of sugar) released into the bloodstream from the liver and increases the body's use of the glucose. Metformin as well as standard of care diet and exercise education is known to lower blood sugar. However, chemotherapy may accelerate metabolic disorders, such as high blood sugar, and the impact of metformin in these breast cancer survivors is not known. Giving metformin with usual care may be more effective than usual care alone in preventing or reversing insulin resistance in women with stage I-III breast cancer after 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.