Phytoestrogens and Breast Cancer

Numerous epidemiological studies suggest that diets rich in phytoestrogens (PE), particularly soy and unrefined grain products, may be associated with low risk of some cancers, especially steroid hormone-dependent, e.g. breast and prostate cancers. Epidemiological, in vitro, animal and human studies have investigated the mechanisms involved in PE biological actions, including steroid hormone activity, effects on cell growth, antioxidant activities, inhibition of chemical carcinogenesis and influences on modulators of cancer risk. The question of whether PE may be used as an anticancer therapeutic and/or chemopreventive agents remains unanswered. Clearly, much more information is required, especially concerning the safety of their use. It seems extremely difficult to predict the effects of various PE mixtures present in different human diets. Long-term studies (in vitro, animal, clinical and epidemiological) with well standardized PE preparations are necessary to assess the potential beneficial and adverse effects. With our current state of knowledge, we cannot conclude whether consumption of soy, SIF (soy isoflavones)supplemented food or the use of particular isoflavones as therapeutics will have positive, null or even adverse effects on cancer (particularly, steroid hormone-dependent) risk and treatment. A brief review of the effects (preventive, antitumor as well as carcinogenic and tumor-stimulating) of PE on various tumor types is presented. Phytoestrogens and Breast Cancer Epidemiological data. Numerous epidemiological studies suggest that diets rich in phytoestrogens (PE), particularly soy and unrefined grain products, may be associated with low risk of some cancers, especially steroid hormonedependent, e.g. breast and prostate cancers (1, 2). Nevertheless, the association between soy food intake and breast cancer risk is controversial. Although isoflavones, such as those found in soy, have been shown to inhibit breast cancer in laboratory studies, correlations between the consumption of isoflavone-containing foods and breast cancer risk have been inconsistent in epidemiological studies. Several studies have indicated that countries with the highest PE consumption have the lowest rates of breast cancer, but other epidemiological studies suggest the lack of a causative relationship. No studies, however, have found an increased risk of breast cancer with increased soy consumption (1). A population-based, case-control study of breast cancer among Chinese, Japanese and Filipino women in Los Angeles was undertaken to further investigate the role of soy. The primary objective was to quantify breast cancer risks associated with the intake of soy during adolescence and adult life among Asian-American women. The risk of breast cancer was significantly inversely associated with soy intake during adolescence and adult life. After adjusting for age, specific Asian ethnicity, education, migration history and menstrual and reproductive factors, women who reported soy intake at least once per week during adolescence showed a significantly reduced risk of breast cancer. There was also a significant trend of decreasing risk with increasing soy intake during adult life. When one considers soy intake during both adolescence and adult life, subjects who were high soy consumers during both time2357 Correspondence to: Adam Opolski, PhD, Department of Experimental Oncology, Institute of Immunology and Experimental Therapy, 12 R. Weigla St., 53-114 Wroclaw, Poland. Tel: 4871/33711-72, Fax: 4871/3371172 ext. 366, e-mail: [email protected]