The analysis of experimental, clinical and epidemiological data on the phytoestrogen properties of the components of flaxseed Linum Usitatissimum L., especially lignans and products of their biotransformation in humans and animals enterodiol (END) and enterolactone (ENL) are presented. Flaxseed is the richest in the vegetable world source of lignans (up to 0,7-1,5% of dry weight of seed), among which prevails secoisolariciresinol diglycoside (SIR-DG). Plant lignans are characterized as natural phytoestrogen that reduce the risk of hormonedependent cancers of breast, uterus and prostate. Anticancerogenic activity of flaxseed lignans due to antioxudant effect END and ENL in the human body. The antioxidant activity of SIR, END, ENL and SIR-DG is higher than that of vitamin E and the antioxidant activity of SIR, END and ENL higher than SIR-DG. On the basis of evidence-based biomedical researches on various models in experimental carcinogenesis, on the tumor cells in vitro, in clinical trials in patients with hormone-dependent tumors, and, finally, in epidemiological studies have proved the anticarcinogenic activity of the components of the flaxseed and validity of recommendations for preventive and curative use in hormone-dependent tumors.