A few studies regarding soy phytoestrogens and breast cancer:
1978
Martin PM and others. Phytoestrogen interaction with estrogen receptors in human breast cancer cells. Endocrinology 1978 Nov;103(5):1860-7. Phytoestrogens “translocate the cytoplasmic estrogen receptor and bind to unfilled nuclear estrogen receptors in whole cells. Bound nuclear receptors are then processed in a manner similar to estradiol in a step, which rapidly decreases total cellular estrogen receptors. The phytoestrogens are also biologically active; they can markedly enhance tumor cell proliferation.”
1996
Petrakis NL and others. Stimulatory influence of soy protein isolate on breast secretion in pre-and postmenopausal women. Cancer Epidemiol Biomarkers Prev 1996 Oct;5(10):785-794. Twenty-four normal pre- and postmenopausal white women, ages 30 to 58 were studied for one year. During months 4-9, the women ingested 38 g soy protein isolate containing 38 mg genistein. Seven of the 24 women developed epithelial hyperplasia during the period of soy feeding, a condition that presages breast cancer. The authors noted that “the findings did not support our a priori hypothesis” that soy protected Asian women against breast cancer. “Instead, this pilot study indicates that prolonged consumption of soy protein isolate has a stimulatory effect on the pre-menopausal female breast, characterised by increased secretion of breast fluid, the appearance of hyperplastic epithelial cells and elevated levels of plasma estradiol. These findings are suggestive of an estrogenic stimulus from the isoflavones genistein and diadzein contained in soy protein isolate.”
1997
Dees C and others. Dietary estrogens stimulate human breast cells to enter the cell cycle. Environ Health Perspect 1997 Apr;105 (Suppl 3):633-636. Dietary estrogens were found to increase enzymatic activity leading to breast cancer. “Our findings are consistent with a conclusion that dietary estrogens at low concentrations do not act as anti-estrogens, but act like DDT and estradiol to stimulate human breast cancer cells to enter the cell cycle.”
1997
Wang C and Kurzer MS. Phytoestrogen concentration determines effects on DNA synthesis in human breast cancer cells. Nutr Cancer 1997;28(3):236-47. Although high levels of isoflavones inhibited DNA synthesis in human breast cancer cells, low levels of genistein and related compounds. . . induced DNA synthesis 150-235%. “The current focus on the role of phytoestrogens in cancer prevention must take into account the biphasic effects observed in this study, showing inhibition of DNA synthesis at high concentrations but induction at concentrations close to probable levels in humans.”
1997
Connolly JM and others. Effects of dietary menhaden oil, soy, and a cyclooxygenase inhibitor on human breast cancer cell growth and metastasis in nude mice. Nutr Cancer 1997;29(1):48-54. Phytoestrogens at levels close to probable levels in humans were found to stimulate cellular changes leading to breast cancer.
1997
Wang C and Kurzer MS. Phytoestrogen concentration determines effects on DNA synthesis in human breast cancer cells. Nutr Cancer 1997;28(3):236-47. Soy intake caused larger mammary fat pad tumors to occur in mice. Soy feeding appeared to suppress enzymes protective of breast cancer.
1997
Anderson D and others. Effect of various genotoxins and reproductive toxins in human lymphocytes and sperm in the Comet assay. Teratog Carcinog Mutagen 1997;17(1):29-43. Human sperm exposed to the phytoestrogen diadzein had reduced DNA integrity. “The integrity of DNA is necessary not only for the noncancerous state, but also for the accurate transmission of genetic material to the next generation.”
1998
Morris SM and others. p53, mutations, and apoptosis in genistein-exposed human lymphoblastoid cells. Mutat Res 1998 Aug 31;405(1):41-56. In vitro administration of genistein was found to cause cellular damage and death. “Our results may be interpreted that genistein is a chromosomal mutagen.”
2000
Habito RC and others. Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males. Br J Nutr 2000 Oct;84(4):557-63. Men consuming tofu instead of meat for 4 weeks had lower testosterone-oestradiol ratios as well as changes in other hormone levels. “Thus, replacement of meat protein with soyabean protein, as tofu, may have a minor effect on biologically-active sex hormones which could influence prostate cancer risk.”
2001
de Lemos ML. Effects of soy phytoestrogens genistein and daidzein on breast cancer growth. Ann Pharmacother 2001 Sep;35(9):118-21. “Genistein and daidzein may stimulate existing breast tumor growth and antagonize the effects of tamoxifen. Women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products.”
2001
Ju YH and others. Physiological concentrations of dietary genistein dose-dependently stimulate growth of estrogen-dependent human breast cancer (MCF-7) tumors implanted in athymic nude mice. J Nutr 2001 Nov;131(11):2957-62. Genistein stimulated breast tumor growth and cell proliferation in mice in a dose-responsive manner.
2001
Ju YH and others. Physiological concentrations of dietary genistein dose-dependently stimulate growth of estrogen-dependent human breast cancer (MCF-7) tumors implanted in athymic nude mice. J Nutr 2001 Nov;131(11):2957-62. Genistein stimulated breast tumor growth and cell proliferation in mice in a dose-responsive manner.
2001
den Tonkelaar I and others. Urinary phytoestrogens and postmenopausal breast cancer risk. Cancer Epidemiol Biomarkers Prev 2001 Mar;10(3):223-8. “We were not able to detect the previously reported protective effects of genistein and enterolactone on breast cancer risk in our postmenopausal population of Dutch women.”
2001
Allred CD and others. Dietary genistin stimulates growth of estrogen-dependent breast cancer tumors similar to that observed with genistein. Carcinogenesis 2001 Oct;22(10):1667-73. Genistin, the glycoside form of genistein, is converted to genistein by human saliva. The glycoside genistin, like the aglycone genistein, can stimulate estrogen-dependent breast cancer cell growth in vivo. Removal of genistin or genistein from the diet caused tumors to regress.
2002
Newbold R and others. Increased uterine cancer seen in mice injected with genistein, a soy estrogen, as newborns. Cancer Research 2002 Jun 1;61(11):4325-8. Infant mice given genistein developed cancer of the uterus later in life. “The data suggest that genistein is carcinogenic if exposure occurs during critical periods in a young animal’s development.”
2003
Tsutsui T and others. Cell-Transforming Activity And Mutagenicity of 5 Phytoestrogens In Cultured Mammalian Cells. Int J Cancer 2003 105, 312-320. Phytoestrogens, such as Genistein and Dadzein, are responsible for the mutation of genes in mammals.
2004
Grace P and others. Phytoestrogen concentrations in serum and spot urine as biomarkers for dietary phytoestrogen intake and their relation to breast cancer risk in European prospective investigation of cancer and nutrition-norfolk. Cancer Epidemiol Biomarkers Prev. 2004 May;13(5):698-708. Women who had high concentration of Phystoestrogens were more likely to be at risk for breast cancer.
2010
Ward H and others. Breast, colorectal, and prostate cancer risk in the European Prospective Investigation into Cancer and Nutrition-Norfolk in relation to phytoestrogen intake derived from an improved database. American Journal of Clinical Nutrition 2010 Feb;91(2):440-8. “Dietary phytoestrogens may contribute to the risk of colorectal cancer among women and prostate cancer among men.”