Metformin Hydrochloride in Preventing Breast Cancer in Patients With Atypical Hyperplasia or In Situ Breast Cancer

Inclusion Criteria

• •Must be at increased risk for breast cancer, defined as at least one of the following four criteria:
• •* Having had a prior biopsy demonstrating atypical hyperplasia, lobular carcinoma in situ (LCIS), or ductal carcinoma in situ (DCIS)
• •* A Gail Model Risk of \>= 1.66% over 5 years
• •* A strong family history of breast and/or ovarian cancer which is defined as at least one of the following:
• •* One first-degree relative with breast cancer before the age of 50 years
• •* One first degree relative with bilateral breast cancer
• •* Two or more first-degree relatives with breast cancer
• •* One first degree relative and two or more second or third degree relatives with breast cancer
• •* One first-degree relative with breast cancer and one or more relatives with ovarian cancer
• •* Two second or third degree relatives with either breast cancer and one or more with ovarian cancer
• •* One second or third degree relative with breast cancer and two or more with ovarian cancer
• •* Three or more second or third degree relatives with breast cancer
• •* Known breast cancer (BRCA)1 or BRCA2 mutation carrier providing that the woman has
• •* Met with a genetic counselor to review genetic testing results, and
• •* Has been offered the opportunity to undergo prophylactic mastectomy and oophorectomy
• •Digital mammogram within 365 days prior to pre-registration
• •Mammograms must be read as not suspicious for breast cancer (American College of Rheumatology \[ACR\] class I-III); subjects with a class IV mammogram may be enrolled once they have been evaluated by a breast surgeon and there is no evidence of invasive malignancy
• •Must be non-pregnant and non-lactating for at least one year prior to pre-registration
• •If currently menstruating, subjects must use a reliable method of birth control
• •Willing to provide RPFNA and blood samples for correlative research purposes
• •Qualifying cytological atypia in RPFNA, Masood score of 14-17; the qualifying RPFNA (of one or both breasts) must be send to Dr. Seewaldt's laboratory for cytological scoring and proteomic analysis; score results must be received from Dr. Seewaldt's lab prior to patient registration/randomization; test must be done =\< 90 days prior to registration/randomization
• •\* Note: Only the contralateral breast can be aspirated in women with DCIS and those undergoing surgery for an atypical lesion; the decision to aspirate the contralateral breast is at the discretion of the woman's surgeon
• •Hemoglobin \>= 9 g/dL
• •Absolute neutrophil count (ANC) \>= 1500/mm\^3
• •Platelet count \>= 75,000/mm\^3
• •Creatinine =\< 1.4 mg/dL
• •Total bilirubin =\< 3.0 mg/dL
• •Aspartate transaminase (AST) =\< 3 x upper limit of normal (ULN)
• •Alanine transaminase (ALT) =\< 3 x ULN
• •Negative pregnancy test done =\< 7 days prior to registration/randomization, for women of childbearing potential only
• •\* A female of childbearing potential is a sexually mature female who: 1) has not undergone a hysterectomy or bilateral oophorectomy; or 2) has not been naturally postmenopausal for at least 12 consecutive months (i.e., has had menses at any time in the preceding 12 consecutive months)
• •Women eligible to take tamoxifen must be offered tamoxifen prevention as part of their clinical care and have refused tamoxifen treatment