Isoflavonoids and Breast Cancer Risk Michelle D. Holmes, MD, DrPH harvard.edu

Learning Objectives To understand the structure and food sources of isoflavonoids To understand the different types of research studies supporting an isoflavonoid-breast cancer link To understand recommendations for soy intake for average risk women and also for women with a personal or family history of breast cancer

Performance Objectives Students should be able to evaluate new research findings on isoflavonoids and breast cancer in light of the previous evidence Be able to make recommendations on soy intake for average risk and high risk women based on the weight of present research evidence

Interests I was trained as a primary care physician and have always had a strong interest in public health. I have always been interested in the impact of diet, exercise, and other lifestyle factors on chronic disease. I became an epidemiologist in mid career. My research focus is diet and cancer.

Overview Structure, food sources of isoflavonoids Different types of studies supporting a isoflavonoid-breast cancer link international in vitro and animal case-control and cohort trials Recommendations

Structure and Food Sources Flavonoids are plant-derived polyphenols Isoflavonoid subgroup weakly estrogenic –examples: genistein, daidzein, equol

Structure of Isoflavonoids and Estradiol Messina, Nutr Cancer 1994;21:113

Intake 1 gram soybeans  2 mg isoflavonoids Typical daily intake: Asian countries  mg Western countries  <1 mg

International Data Asian countries: high soy intake and lower breast cancer rates Japanese migrants assume host country rates of breast cancer Western diet: minimal soy Vegetarians in the US have lower cancer rates

Estrogenic Effects Weakly estrogenic 1/1000 th - 1/100,000 th the strength of estradiol Produce estrogenic responses in mice May be antagonistic by competing for estrogen receptors

What is the evidence that isoflavonoids prevent breast cancer?

In vitro studies of Genistein Inhibits Tyrosine Kinase (important for cell proliferation, transformation) Markovits J, 1989, Cancer Res Linnasier C, 1993, Biochemical Pharmacology Inhibits DNA topoisomerase II (causes DNA breaks) Markovits J, 1989, Cancer Res

In vitro Studies of Genistein Induces Differentiation Constantinou A, 1990, Cancer Res Kando K, 1991, Cancer Res Watanabe T, 1993, Cancer Res Inhibits Angiogenesis Fotis T, 1993, Proc Natl Acad Sci

Length, mm bFGF, µg/L genistein, µmol/L Fotsis,J. Nutr 1995,125;790S Genistein as an Angiogenesis Inhibitor

In vitro Studies of Genistein Affects Growth of ER+ human breast cancer cells: Stimulates at low dose Inhibits at high dose Miodini P, 1999, Br J Cancer Nakagawa H, 2000, J Cancer Res Clin Oncol Inhibits growth of ER- human breast cancer cells Shen F, 1999, Anticancer Res

Animal Studies: Isoflavonoids and Mammary Tumors StudyResults Study Results Carroll, 1975 Null Barnes, 1990  Troll, 1980  Barnes, 1990  Gridley, 1983 Null Constantinou 1998  Hawrylewics, 1989  Fritz, 1998  Hsueh, 1989 Null Hilakivi-Clarke 1999  Baggott, 1990  Hakkak, 2000  Santell, 2000 Null

Weeks after NMU administration Mammary Tumor Incidence in Rats C asein SPI+Met SPI Percent of rats with mammary tumors 0 5 NMU INJECTION DIET CHANGE Casein

Adolescent Soy Intake and Breast Cancer Risk Shu, CEBP cases and 1556 controls in China Diet age by interview Separately asked mothers of 296 cases and 359 controls

Adolescent Diet Quintile of IntakeRR95% CI Total20.75( ) soy30.69( ) foods40.69( ) 50.51( ) p-trend <0.01

Cohort Studies of Soy and Breast Cancer Reference Populations Cases ExposureRR Nomura, 1978 Japanese in HI86 Husbands dietNull Hirayama, 1985 Japan- miso0.46 Key, 1999 Japan 427 tofu, misoNull

Problem:Assessment of dietary isoflavonoids is difficult in epidemiological studies Amoung U.S women, large amounts of isoflavonoids come from “hidden” soy: - soy protein isolate - soy concentrate - soy flour (white bread and donuts) Frequent in processed foods and is brand-dependent Horn-Ross, CCC, 2000

Trials: Does Soy Lower Estrogens? Reference NDuration: MonthsResult Cassidy,  FSH, LH follicular E2 Duncan,  FSH, LH Martini, No change Lu, shifted metabolism to more favorable estrogens metabolites Lu,  progesterone levels Wu,  luteal E2 only in 10 Asian women

Cont’d Reference NDuration: Months Result Duncan,  estrogens only in 5 equol excreters regardless of soy intake Xu, shifted metabolism to more favorable estrogen metabolites

RCTs of Soy and Estrogen Nagata, 1998 Hi/Low SoyDuration/monthsResults 31/29 2  E2 and estrone but N.S

Does Soy Increase Breast cell Proliferation? McMichael-Phillips, AJCN, RCT of 48 premenopausal women scheduled for breast biopsy - 2 weeks soy supplemented diet - Normal breast tissue labelled for markers of proliferation - High soy group had  proliferation Hargreoues, J Clin Endoc Metab, Sequential trial of 84 premenopausal women - Underwent nipple aspiration (NA) -  markers of proliferation in NA fluid after soy intake

Does Soy Increase Breast cell Proliferation? Maskarinec, Br Cancer Res, Cross-sectional study in HI - Soy intake assessed by questionnaire vs. density on mammogram -Results: - High soy  density - High soy  breast size

Hypothesis: Could early-life soy exposure induce early breast maturation making it resistant to carcinogenesis? Evidence: Isoflavonoids promote differentiation in vitro Some animal studies have shown large effects with pre-pubertal exposure International differences persist until 2nd generation Shu, 2001 case-control study of adolescent soy intake

Isoflavonoids and Breast Cancer Risk: Conclusions Biologically plausible: –estrogenic effects –effects on angiogenesis, cell growth Animal data suggestive Epidemiologic data suggestive but cohort studies are poor Adverse effects possible, balance between proestrogen/anti estrogen effects is unclear

What should clinicians recommend? –Modest intake of soy products similar to Asian cultures (1-2 servings/day) unlikely to be harmful in the average women and may be helpful –Many clinicians, NCI website suggest that high risk women avoid soy: Women with breast cancer, particularly ER+ or on tamoxifen Women with a strong family history