Metformin and Omega-3 Fatty Acids in Woman With a History of Early Stage Breast Cancer

Inclusion Criteria:

History of histologically-confirmed stage 0, I, II, or III breast carcinoma without evidence of disease at trial entry. Participants with a resected local recurrence are eligible
Minimum of 6 months since last chemotherapy, biologic therapy (i.e., trastuzumab), radiation therapy, and/or breast surgery and no evidence of recurrent disease
Minimum of 6 months since completion of adjuvant tamoxifen (tamoxifen is known to lower mammographic density119-121). Current use of a third generation aromatase inhibitor [AI] (i.e., anastrozole, letrozole, exemestane) is permitted provided that the participant has been on a stable dose for the past 6 months
Age 21 to 75 years. Both pre- and postmenopausal women will be included in this study. We will exclude perimenopausal women, defined as menstrual cycle irregularity (variable cycle length that differs from normal by more than 7 days) and an Follicle-Stimulating Hormone (FSH) greater than 20 mili international units
Negative serum pregnancy testing
Normal mammogram of the contralateral breast within the past 12 months, defined as no new suspicious calcifications or other abnormal findings warranting a breast biopsy
Eastern Cooperative Oncology Group (ECOG) performance status less than 2
Participants must have normal organ and marrow function within 28 days prior to randomization
Body mass index (BMI) greater than or equal to 25 kilograms per meter squared or baseline fasting glucose of less than 126 milligrams per deciliter
Participants must have a baseline mammographic density greater than or equal to 25 percent based upon the Breast Imaging Reporting and Data System (BIRADS) density score of 2, 3, or 4. Women with a baseline mammographic density of less than 25 percent (BIRADS Score= 1) will not be eligible
Willingness to abstain from all omega-3 fish oil supplements for 30 days prior to baseline evaluation and during the study intervention
Willingness to comply with all study interventions and follow-up procedures
Ability to understand and willingness to sign a written informed consent document

Exclusion Criteria:

History of histologically-confirmed bilateral breast cancer
History of or plans for bilateral mastectomies
Evidence of metastatic breast cancer
Prior radiation therapy or implant in the contralateral breast
Known diabetes (type 1 or 2) or baseline fasting glucose greater than 126 milligrams per deciliter
Any condition associated with increased risk of metformin-associated lactic acidosis (e.g., congestive heart failure defined as New York Heart Association [NYHA] Class III or IV functional status, history of acidosis of any type, intake of 3 or more alcoholic beverages per day on average over the past 6 months)
Currently taking metformin, sulfonylureas, thiazolidinediones, or insulin for any reason
History of allergic reactions attributed to compounds of similar chemical or biologic composition to metformin or omega-3 fatty acids
Receiving hormone replacement therapy, tamoxifen, or raloxifene within 6 months of trial entry
Participants may not be receiving any other investigational agents for 30 days prior to baseline evaluation and during the study intervention
Any omega-3 fatty acids should not be taken for 30 days prior to baseline evaluation and during the study intervention. If participants are consuming any of these items and would like to participate in this study, then a 30-day washout period will be required. - Uncontrolled or significant co-morbid illness patients receiving active chemotherapy or radiotherapy; or psychiatric illness/social situations that would limit compliance with study requirements