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Home Prevention Can eating Soy products cause recurrence of Breast Cancer?

Can eating Soy products cause recurrence of Breast Cancer?

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Can eating Soy products cause recurrence of Breast Cancer?


Can eating Soy products cause recurrence of Breast Cancer? At the 102nd Annual AACR conference a question that lingers in most Breast cancer survivors was answered favorably for Soy lovers. And the much awaited conclusion was that ‘Soy food consumption was not associated with an increased risk of mortality or cancer recurrence among breast cancer survivors’ [1].


“It’s hard enough these days to find foods that people like that are also healthy for them, and this issue has, on occasion, really stressed out vegetarians,” said Dr. Jennifer Griggs, MD, MPH, director of the breast cancer survivorship program at the University of Michigan’s Comprehensive Cancer Center, in Ann Arbor. “I think we can be comfortable now telling them not to worry.” [2]


This study by Sarah J. Nechuta et al combined cohorts of women diagnosed with invasive breast cancer from U.S. and Shanghai, China. A remarkable number of 16,048 women were included in the analysis. An average follow-up of 9.2 years led to this conclusion that Soy consumption was not associated with an increasing recurrence of Breast cancer or increasing mortality [1].


“Our results indicate it may be beneficial for women to include soy food as part of a healthy diet, even if they have had breast cancer,” said lead investigator Xiao Ou Shu, professor of medicine, Vanderbilt-Ingram Cancer Center. “This cannot be directly generalized to soy supplements, however, as supplements may differ from soy foods in both the type and amount of isoflavones.” [3]





In the United States, 1 in 8 women develop invasive breast cancer. In 2010, 207,090 new cases of invasive breast cancer were expected to be diagnosed of which about 39,840 were expected to die due to this disease [4].


From 1999 to 2006, death rates due to Breast cancer have declined and in 2010 there were more than 2.5 million breast cancer survivors in U.S. [4]. This decrease can be attributed to advances in the treatment options and also to the reduced use of Hormonal Replacement Therapy among older women. Prolonged estrogen exposure has been described as a probable risk factor in the development of Breast cancer [5].


Following treatment each breast cancer patient is provided with a survivorship care plan regarding the patient’s treatment summary and the regimen for follow up. Unfortunately, guidelines regarding diet are vague.


We will explore often asked questions regarding Soy products, other foods and evidence for effects of these on Breast Cancer recurrence.



What are estrogens?


Estrogens are a set of compounds found in humans and other animals which serve as the primary female sex hormone. In the body, estrogen is found in its steroidal form, but there are a variety of non steroidal estrogens found in nature and produced synthetically.


The non-steroidal estrogens found outside the body can be of the following types:


Xenoestrogens – found in synthetically produced substances such as pesticides, Bisphenol A (used in manufaturing plastic), cosmetics, food additives etc.

Phytoestrogens – mainly found in plant products – further can be divided into types such as coumestans, prenylated flavonoids, isoflavones and lignans. Of these the most researched are isoflavones, which soy and red clover have a high content of.

Mycoestrogens – found in fungi, similar structure and action to phytoestrogens.


While Xenoestrogens are known to be carcinogenic [6] there is much debate as to the effect of Phytoestrogens and Mycoestrogens on Breast Cancer.



What are the estrogen rich foods?


Fruits such as – Apples, Apricots, Cherries, Dates, Papaya, Plums, Pomegranates, Pumpkins


Cereals such as – Barley, Rice, Wheat, Oats


Pulses such as – Black eyed peas, chick peas, lima beans, Mung beans, Red beans, Red clover, Rhubarb, Sesame seeds, Soybean sprouts, Soybeans, Split peas, Sunflower seeds, Anise seed, Flax seeds


Vegetables such as – Beets, Broccoli, Carrots, Cucumbers, Eggplants, Garlic, Ginger, Olives, Peas, Peppers, Potatoes, Tomatoes, Yams


Spices such as – Fenugreek, Fennel, Ginseng, Licorice, Oregano, Parsley, Thyme


Nuts such as – Almonds, Peanuts


Other foods such as – Alfalfa, Baker’s yeast, Beer, Bourbon, Dairy products, Eggs, Olive oil



Does Soy/tofu cause Breast Cancer?


Soy and Soy products such as Tofu, Tempeh, Edamame and Soy milk contain high content of phytoestrogens in the form of the isoflavone - genistein and also lignans.


Though the estrogen content is not high enough to produce an estrogenic response in pre-menopausal human receptors, a study in 2006 described that genistein (an isoflavone found in soy) increases the incidence of mammary tissue changes to promote tumor genesis in lab rats [7].


Reviews of literature done over the past two decades have been incongruous with the result varying with geographical location, menopausal status, dosage and time of exposure [8-11]. This has lead to contradictory trends in the popular feelings about Soy intake. There has been a recent trend to discourage Soy consumption among breast cancer survivors.


The recent study by Nechuta et al with both Asian and American women of pre and post menopausal age groups, however, has shown that Soy products are not harmful in either population and does not increase the recurrence of Breast cancer in these patients [1].



Does Soy/tofu prevent Breast Cancer?


In 1996, the structure of isoflavones found in Soy created much interest because in the doses of dietary intake it was supposed to have anti-estrogenic effects which had the potential to have preventive effects on the incidence and recurrence of Breast Cancer [12].


The beneficial effect of Soy in preventing Breast Cancer has been demonstrated in the Asian population but higher dietary intake of Soy and early exposure during the pre-pubertal years are probable factors that put the Asian population at an advantageous position as compared to American women [13-15].


The study by Nechuta et al has shown that while there is no increased incidence of Breast Cancer among women who eat soy products, the beneficial effect is significant only in the Asian population [1]. However, the effect of Soy in preventing Breast cancer recurrence in ER negative cancers is not described exclusively.



What is the effect of Soy on Health?


Soy products have been studied to have beneficial effects on other aspects of health such as:

It has been shown to have a therapeutic effect in prostate cancer by causing the death of prostate cancer cells [16-17].


There are studies describing beneficial effects of Soy in colon cancer by attenuating the tumor progression [18-19].


Soy products have been shown to reduce cholesterol levels and hence have a beneficial effect on both cardiovascular system and also a role in non-alcoholic fatty liver [20-23].


There have been studies to suggest the beneficial effect of estrogen in tissue repair following brain injury in the form of stroke; studies are underway to study whether soy products exhibit a similar role [24-26].



What other food products have an effect on Breast Cancer?

Studies have shown that dietary intake of common mushrooms decreases the incidence of breast cancer by 50% [27-28].


Literature also shows that combined intake of mushrooms and green tea decreases the incidence of Breast cancer by 90% [28].


There is also a study which describes the role of green leafy vegetables which belong to the Brassica family such as cabbage, cauliflower, kale, brussels, broccoli in decreasing the incidence of breast cancer [29-30].


Though few studies have reported the beneficial effect of lycopene in tomatoes in preventing breast cancer, the findings are inconclusive [31-33].





A healthy lifestyle with a low fat diet and exercise has been described as the most probable reason the Asian population is at a lower risk of developing breast cancer than the Western population. Early consumption of Soy in pre-pubertal age with a high dietary intake also maybe factors that have resulted in a proven beneficial effect of Soy products in preventing Breast Cancer in the Asian population.


Though it is early to deliver a conclusive report on the effects of Soy on Breast Cancer, it has been shown not to increase the recurrence rate of Breast Cancer[1]. The beneficial effect in preventing recurrences, however, is yet to be consolidated.


Soy products have been proven to have several beneficial effects in other cancers and diseases.

Mushrooms and green tea seems to have a beneficial effect by preventing incidence of Breast Cancer while, further studies are required to warrant the effects of green leafy vegetables and tomatoes in preventing Breast Cancer.


Artificial soy products and additives however are best avoided as synthetic estrogens are more likely to be carcinogenic.



Reference List


1.       Nechuta, S.J., Postdiagnosis soy food intake and breast cancer survival: Report from the After Breast Cancer Pooling Project : Abstract number 4665, in American Association of Cancer Research 102nd Annual Meeting 2011 2011: Florida.

2.       Shaw, G. Dietary Soy Found Safe for Breast Cancer Survivors. JUNE 2011; Available from: http://www.clinicaloncology.com/ViewArticle.aspx?d=Solid+Tumors&d_id=148&i=June+2011&i_id=734&a_id=17227.

3.       Stuart, D. Soy foods not a risk for breast cancer survivors. Apr. 12, 2011; Available from: http://news.vanderbilt.edu/2011/04/soy-foods-breast-cancer-survivors/.

4.       April 19, 2011; Available from: http://www.breastcancer.org/symptoms/understand_bc/statistics.jsp.

5.       Yager, J.D. and N.E. Davidson, Estrogen carcinogenesis in breast cancer. N Engl J Med, 2006. 354(3): p. 270-82.

6.       Starek, A., Estrogens and organochlorine xenoestrogens and breast cancer risk. Int J Occup Med Environ Health, 2003. 16(2): p. 113-24.

7.       Padilla-Banks, E., W.N. Jefferson, and R.R. Newbold, Neonatal exposure to the phytoestrogen genistein alters mammary gland growth and developmental programming of hormone receptor levels. Endocrinology, 2006. 147(10): p. 4871-82.

8.       Enderlin, C.A., et al., Dietary soy intake and breast cancer risk. Oncol Nurs Forum, 2009. 36(5): p. 531-9.

9.       Trock, B.J., L. Hilakivi-Clarke, and R. Clarke, Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst, 2006. 98(7): p. 459-71.

10.   Wu, A.H., et al., Epidemiology of soy exposures and breast cancer risk. Br J Cancer, 2008. 98(1): p. 9-14.

11.   Shu, X.O., et al., Soy food intake and breast cancer survival. JAMA, 2009. 302(22): p. 2437-43.

12.   Lu, L.J., et al., Effects of soya consumption for one month on steroid hormones in premenopausal women: implications for breast cancer risk reduction. Cancer Epidemiol Biomarkers Prev, 1996. 5(1): p. 63-70.

13.   Butler, L.M., et al., A vegetable-fruit-soy dietary pattern protects against breast cancer among postmenopausal Singapore Chinese women. Am J Clin Nutr, 2010. 91(4): p. 1013-9.

14.   Kim, E.Y., et al., Comparisons of food intake between breast cancer patients and controls in Korean women. Nutr Res Pract, 2007. 1(3): p. 237-42.

15.   Wu, A.H., et al., Green tea, soy, and mammographic density in Singapore Chinese women. Cancer Epidemiol Biomarkers Prev, 2008. 17(12): p. 3358-65.

16.   Szliszka, E. and W. Krol, Soy isoflavones augment the effect of TRAIL-mediated apoptotic death in prostate cancer cells. Oncol Rep, 2011. 26(3): p. 533-41.

17.   Lazarevic, B., et al., Efficacy and Safety of Short-Term Genistein Intervention in Patients with Localized Prostate Cancer Prior to Radical Prostatectomy: A Randomized, Placebo-Controlled, Double-Blind Phase 2 Clinical Trial. Nutr Cancer, 2011.

18.   Tsai, C.Y., et al., Effect of soy saponin on the growth of human colon cancer cells. World J Gastroenterol, 2010. 16(27): p. 3371-6.

19.   Qi, W., et al., Genistein inhibits proliferation of colon cancer cells by attenuating a negative effect of epidermal growth factor on tumor suppressor FOXO3 activity. BMC Cancer, 2011. 11(1): p. 219.

20.   Esteves, E.A., et al., Modified Soybean Affects Cholesterol Metabolism in Rats Similarly to a Commercial Cultivar. J Med Food, 2011.

21.   Huang, Z., et al., [Changes of serum lipids after soy isoflavone and calcium supplementation in postmenopausal Chinese women with different ER-beta genotypes]. Wei Sheng Yan Jiu, 2011. 40(3): p. 280-2.

22.   Ishiguro, T., et al., Cholesterol-lowering effect of kori-tofu protein and its high-molecular-weight fraction content. Biosci Biotechnol Biochem, 2011. 75(3): p. 575-7.

23.   Takahashi, Y. and T. Konishi, Tofu (soybean curd) lowers serum lipid levels and modulates hepatic gene expression involved in lipogenesis primarily through its protein not isoflavone component in rats. J Agric Food Chem, 2011.

24.   Schreihofer, D.A. and L. Redmond, Soy phytoestrogens are neuroprotective against stroke-like injury in vitro. Neuroscience, 2009. 158(2): p. 602-9.

25.   Ma, T.C., et al., A large-scale chemical screen for regulators of the arginase 1 promoter identifies the soy isoflavone daidzeinas a clinically approved small molecule that can promote neuronal protection or regeneration via a cAMP-independent pathway. J Neurosci, 2010. 30(2): p. 739-48.

26.   Ma, Y., J.C. Sullivan, and D.A. Schreihofer, Dietary genistein and equol (4', 7 isoflavandiol) reduce oxidative stress and protect rats against focal cerebral ischemia. Am J Physiol Regul Integr Comp Physiol, 2010. 299(3): p. R871-7.

27.   Hong, S.A., et al., A case-control study on the dietary intake of mushrooms and breast cancer risk among Korean women. Int J Cancer, 2008. 122(4): p. 919-23.

28.   Zhang, M., et al., Dietary intakes of mushrooms and green tea combine to reduce the risk of breast cancer in Chinese women. Int J Cancer, 2009. 124(6): p. 1404-8.

29.   Terry, P., et al., Brassica vegetables and breast cancer risk. JAMA, 2001. 285(23): p. 2975-7.

30.   Smiechowska, A., A. Bartoszek, and J. Namiesnik, [Cancer chemopreventive agents: glucosinolates and their decomposition products in white cabbage (Brassica oleracea var. capitata)]. Postepy Hig Med Dosw (Online), 2008. 62: p. 125-40.

31.   Friedman, M., et al., Tomatine-containing green tomato extracts inhibit growth of human breast, colon, liver, and stomach cancer cells. J Agric Food Chem, 2009. 57(13): p. 5727-33.

32.   Wang, H. and L.K. Leung, The carotenoid lycopene differentially regulates phase I and II enzymes in dimethylbenz[a]anthracene-induced MCF-7 cells. Nutrition, 2010. 26(11-12): p. 1181-7.

33.   Froufe, H.J., R.M. Abreu, and I.C. Ferreira, Using molecular docking to investigate the anti-breast cancer activity of low molecular weight compounds present on wild mushrooms. SAR QSAR Environ Res, 2011. 22(3): p. 315-28.



Shenthol Sasankan ,

Visiting Medical student at UIC,

Kasturba Medical College, Mangalore, India


Divyesh G Mehta MD