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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
InterestsI 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 50-100 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 1/1000th -1/100,000th 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 DifferentiationConstantinou A, 1990, Cancer Res
Kando K, 1991, Cancer Res
Watanabe T, 1993, Cancer Res
• Inhibits AngiogenesisFotis T, 1993, Proc Natl Acad Sci
0
1
2
3
4
5
Length,mm
bFGF, µg/L 0 30 30 30 30genistein, µmol/L 0 0 50 100 200
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
Study Results 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
Casein
SPI+Met
SPI
Percent of rats w
ith mam
mary tum
ors
0 5
NMU INJECTION
DIETCHANGE
268
100
10
Casein
Reference,Population
N cases Exposure RR (95% CI)
Hirohata, 1985Japan
212 Soybeans — Null
Lee, 1991Singapore
200 Soy protein 0.39 (0.19, 0.80)
Hirose, 1995Japan
1186 Bean curd 0.81 (0.65, 0.99)
Wu, 1996US (Asian women)
597 Total soy 0.85 (0.74, 0.99)
Ingram, 1997Australia
144 Equol* 0.27 (0.10, 0.69)
Zheng, 1999China
60 Isoflavanoid 0.14 (0.02-0.88)
Shu, 2001China
1459 AdolescentTotal Soy
0.51 (0.40-0.65)
*Measured in urine
Adolescent Soy Intake and Breast Cancer Risk
Shu, CEBP 2001
• 1459 cases and 1556 controls in China
• Diet age 13-15 by interview
• Separately asked mothers of 296 cases and 359 controls
Adolescent Diet
Quintile of Intake RR 95% CI
1 1.00 -
Total 2 0.75 (0.60-0.93)
soy 3 0.69 (0.55-0.87)
foods 4 0.69 (0.55-0.86)
5 0.51 (0.41-0.65)
p-trend <0.01
Cohort Studies of Soy and Breast Cancer
Reference Populations Cases Exposure RR
Nomura, 1978 Japanese in HI 86 Husbands diet Null
Hirayama, 1985 Japan - miso 0.46
Key, 1999 Japan 427 tofu, miso Null
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 N Duration: Months ResultCassidy, 1994 6 1 FSH, LH
follicular E2
Duncan, 1999 14 3 FSH, LH
Martini, 1999 36 2 No change
Lu, 2000 8 1 shifted metabolism to more favorable estrogens metabolites
Lu, 2000 10 1 progesterone levels
Wu, 2000 20 7 luteal E2 only in 10 Asian women
Cont’d
Reference N Duration: Months Result
Duncan, 2000 14 - estrogens only in 5 equol excreters regardless of soy intake
Xu, 2000 18 9 shifted metabolism to more favorable
estrogen metabolites
RCTs of Soy and Estrogen
Nagata, 1998 Hi/Low Soy Duration/months Results
31/29 2 E2 and estrone
but N.S
Does Soy Increase Breast cell Proliferation?
McMichael-Phillips, AJCN, 1998
- 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, 1999
- 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, 2001
- 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