Phase II Study of Metformin for Reduction of Obesity-Associated Breast Cancer Risk

Inclusion Criteria:

* Premenopausal women
* 21-54 years of age
* Have a BMI of 25 kg/m2 or greater
* No change in menstrual patterns for the past 6 months preceding the time of registration
* Waist circumference ≥ 35 inches or ≥ 31 inches for Asian Americans, individuals with polycystic ovary syndrome, or individuals with non-alcoholic fatty liver disease.
* Have at least one other component of metabolic syndrome (103) reported below:

  * Elevated triglycerides (≥ 150 mg/dL (1.7 mmol/L) or on drug treatment for elevated triglycerides
  * Reduced HDL-C (\< 50 mg/dL (1.3 mmol/L) or on drug treatment for reduced HDL-C
  * Elevated blood pressure (≥ 130 Hg systolic blood pressure or ≥85 mm Hg diastolic blood pressure or on antihypertensive drug treatment in a patient with a history of hypertension
  * Elevated fasting glucose (≥100 mg/dL)
* Mammogram negative for breast cancer within the 12 months preceding the time of registration for women ≥ 50 years of age
* Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

* Postmenopausal women

  * Amenorrhea for at least 12 months (preceding the time of registration), or
  * History of hysterectomy and bilateral salpingo-oophorectomy, or
  * At least 55 years of age with prior hysterectomy with or without oophorectomy, or
  * Age 35 to 54 with a prior hysterectomy without oophorectomy OR with a status of ovaries unknown with documented follicle-stimulating hormone level demonstrating elevation in postmenopausal range
* Women who are pregnant, planning pregnancy within the next year, or breastfeeding
* On treatment with any drug for diabetes
* Have uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or any illness that would limit compliance with study requirements
* Have received chemotherapy and/or radiation for any malignancy (excluding non-melanoma skin cancer and cancers confined to organs with removal as only treatment) in the past 5 years (preceding the time of registration)
* Have received other investigational agents within the past 3 months (preceding the time of registration)
* Have a history of lactic acidosis or risk factors for lactic acidosis
* Have significant renal disease or dysfunction (creatinine ≥ 1.4 mg/dL)
* Have significant hepatic dysfunction (bilirubin ≥ 1.5 x ULN unless with Gilberts syndrome or AST/ALT ≥ 3 x ULN)
* Have a history of alcoholism or high alcohol consumption (average of \> 3 standard drinks/day)
* Have a history of allergic reactions to metformin or similar drugs
* Have a history of severe claustrophobia
* Have electrically, magnetically, or mechanically activated implants including cardiac pacemaker, cochlear implants, magnetic surgical clips or prostheses
* Have breast implants