Metformin Hydrochloride and Lifestyle Intervention in Improving Biomarker Levels in Blood Samples From Stage I-IIIA Breast Cancer Survivors

Inclusion Criteria

• Overweight or obese (body mass index [BMI] >= 25.0 kg/m^2)
• Post-menopausal at time of diagnosis
• Diagnosis of stage I-IIIA breast cancer within past 5 years (confirmed by medical record review)
• Treatment with total mastectomy and axillary dissection; or breast-sparing surgical removal of cancer with clear macroscopic margins and axillary dissection; followed by adjuvant breast radiation
• Not currently undergoing or planning to initiate chemotherapy
• If undergoing adjuvant therapy (e.g. tamoxifen or aromatase inhibitors) willing and able to remain on current regimen for entire 6-month study period
• Ability to attend clinic visits
• Accessible geographically and by telephone
• Able to communicate dietary and physical activity data via telephone
• Fluent in English
• ELIGIBILITY CRITERIA FOR NORMAL-WEIGHT WOMEN IN PILOT STUDY
• Normal weight (BMI < 25.0 kg/m^2)
• Must be weight stable, as defined by staying within 10 percent of their current weight for 6 months
• Participants who were eligible for the main trial with the exception of not meeting BMI criteria for obesity

Exclusion Criteria

• Renal insufficiency (i.e., serum creatinine outside of normal limits)
• Liver impairment or congestive heart failure
• Daily treatment with thiazides or β-blockers (exclusion only if < 3 months)
• Diabetes being treated with other than diet and lifestyle
• Hormone therapy, including vaginal estrogen creams
• Other primary or recurrent invasive cancer within the last 10 years (other than nonmelanomic skin cancer or carcinoma of the cervix in situ)
• Inability to commit to the intervention schedule
• Any condition that, in the investigators’ judgment, would contraindicate diet modification, increased physical activity, use of metformin, or otherwise interfere with participation in the trial