Key Findings:
This comprehensive review paper from the University of Toronto provides a summary of animal studies, the majority (13 of the 18 reviewed here) of which suggest that whole milled flaxseed and it constituents may prevent and reduce the growth of breast tumors. In eleven of 12 studies, flax SDG also found beneficial effects as did seven trials on flax oil. Levels assessed in animal models equate to about 25–50 g of flaxseed, 10–20 g of flax oil, and 25–50 mg of SDG for humans depending on how much other food they eat. Initial studies in women do show potential of reducing and/or alleviating biomarkers of breast cancer. The investigators have reported beneficial interaction of flaxseed, oil and SDG with breast cancer drugs, such as tamoxifen and trastuzumab.
ABSTRACT:
Flaxseed (FS), rich in the phytoestrogen lignans and alpha-linolenic acid-rich oil, has been suggested to have an anticancer effect. Questions remain whether FS and its lignan and oil components are effective in reducing breast cancer risk and tumour growth, and can interact beneficially with breast cancer drugs. To find answers, in vitro, animal, observational, and clinical studies on FS and its lignan and oil components were reviewed. The majority of studies in various rodent models show that 2.5%-10% FS diet or the equivalent amount of lignan or oil reduces tumour growth. Ten percent FS and equivalent lignans do not interfere with but rather increase the effectiveness of tamoxifen (80 mg/day) while the 4% FS oil increases trastuzumab/Herceptin (2.5 mg/kg) effectiveness. Observational studies show that FS and lignan intake, urinary excretion, or serum levels are associated with reduced risk, particularly in postmenopausal women. Lignans reduce breast cancer and all-cause mortality by 33%-70% and 40%-53%, respectively, without reducing tamoxifen effectiveness. Clinical trials show that FS (25 g/day with 50 mg lignans; 32 days) reduces tumour growth in breast cancer patients and lignans (50 mg/day; 1 year) reduces risk in premenopausal women. Mechanisms include decreased cell proliferation and angiogenesis and increased apoptosis through modulation of estrogen metabolism and estrogen receptor and growth factor receptor signalling pathways. More clinical trials are needed but current overall evidence indicates that FS and its components are effective in the risk reduction and treatment of breast cancer and safe for consumption by breast cancer patients. (Authors Abstract)