Low Dose Tamoxifen With or Without Omega-3 Fatty Acids for Breast Cancer Risk Reduction

This study is open to:

Women who are ages 45–74, have gone through menopause, are overweight or obese (body mass index of 25 or higher), and meet at least one of the following breast cancer risk criteria:

• Previous breast biopsy or diagnosis: A history of atypical hyperplasia, lobular carcinoma in situ (LCIS), or ductal carcinoma in situ (DCIS). Previous DCIS must have been treated, with treatment completed at least three months before breast tissue sampling.

• Dense breast tissue: Mammograms showing a high level of breast density.

• Inherited genetic mutation in ATM, BARD1, BRCA2, CDH1, CHEK2, NF1, PALB2, PTEN, RAD51C, RAD51D or STK11. 

• Family history of breast cancer: Breast cancer in a first- or second-degree relative before age 50; breast cancer in two or more first- or second-degree relatives; or a close relative with breast cancer in both breasts or with both breast and ovarian cancer.

• Elevated breast cancer risk 

Additional requirements include:

• Having at least one breast that can be used for tissue sampling and has not been treated for cancer.

• Having a recent screening mammogram with results that meet the study's requirements.

• Being able to provide blood samples and undergo breast tissue sampling.

• Being in adequate general health to participate and take the study medications.

• Providing documentation of the breast cancer risk factor used to qualify, such as a genetic test report, breast biopsy report, mammogram report, family history documentation, or risk calculation.

This study is not open to people:

• With a history of invasive breast cancer or uterine cancer, or another invasive cancer that is active or was treated within the past two years. Non-melanoma skin cancer is an exception.

• With a BRCA1 or TP53 inherited mutation.

• With type 1 or type 2 diabetes requiring medication, a history of blood clots, blood clots in the lungs, stroke, gastric bypass surgery, or long-term liver disease.

• Currently breastfeeding or having breastfed within the past 12 months.

• Taking blood thinners; daily aspirin that cannot be safely paused as required for breast tissue sampling; hormone therapy other than permitted low-dose vaginal estrogen; immunosuppressive medications; metformin; certain medications that affect how tamoxifen works; or GLP-1 medications currently being used or planned during the study period.

• With more than two months of prior tamoxifen or similar medications. People who used these medications for less than two months must have stopped them at least six months before starting the study.

• Taking high-dose omega-3 supplementation, more than 1 gram daily within the past six months.

• With breast implants in both breasts as these may interfere with the required breast tissue sampling.

• With a history of allergic reactions to tamoxifen, omega-3 fatty acids, or related products, or other circumstances that could make study participation unsafe or difficult.