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PHYTING BREAST CANCER: ARE
PHYTOESTROGENS A FRIEND OR FOE?
Media reports convey a mixed message about the effects of phytoestrogen consumption on
health, with breast cancer coming under particular scrutiny. To date, studies have yielded
inconclusive results.
Primary Aim
To assess the evidence regarding phytoestrogenic effects upon breast cancer risk in women.
Secondary Aims
1. To critically review literature and identify relevant papers for analysis.
2. To investigate identifiable markers for breast cancer risk in women.
3. To gain further understanding of the underlying mechanisms of phytoestrogen actions on
breast tissue.
To navigate through the website please use the main tabs across the top of the page to locate
and move between the different sections. To access sub-sections of the appendices please use
the drop down menu that appears when the cursor is held above the appendices tab. Clicking
on any diagrams or tables throughout the website will enlarge them.
This site was made by a group of University of Edinburgh medical students who studied this
subject over 10 weeks as part of an SSC2aproject.
This website has not been peer reviewed.
We certify that this website is our own work and that we have authorisation to use
all the content (e.g. figures / images) used in this website.
We would like to thank our tutor Dr Simon Langdon for all his fantastic help with our
project.
Word count minus Contributions page, References page, Critical
Appraisal Appendix, Information Search Report, Word Version
appendix and other sections clearly marked as Appendices: 4,421
Total Website Word count: 17,331
INTRODUCTION
What are phytoestrogens?
Phytoestrogens are plant-derived chemicals that simulate oestrogenic actions in the
body1. There are three main groups of phytoestrogens, namely isoflavones, commonly found
in soy; lignans in seeds and wholegrains; and coumestans in broccoli and sprouts2.
Isoflavones such as genistein and daidzein are also widely marketed as dietary supplements3.
What is the big fuss about?
Besides being used as an alternative to hormone replacement therapy in relieving postmenopausal symptoms, phytoestrogens have been associated with protective effects against
breast cancer, osteoporosis and cardiovascular diseases4. The link between phytoestrogen
consumption and breast cancer in particular, was proposed based on epidemiological studies
comparing Asian and Western women2. Isoflavone-rich diets of East Asian populations5are
believed to be one of the factors contributing to a lower incidence of breast cancer in
countries such as Japan and China, as opposed to countries like the USA6.
How do they work against breast cancer?
Phytoestrogen bioactivity is based on their structural similarity with 17β-estradiol(E2) and
their affinity for oestrogen receptors(ER)7. There are two subtypes of oestrogen receptors,
namely ER- α and ER- β7,8. Phytoestrogens are selective oestrogen receptor
modulators(SERMs) where their actions vary with factors such as phytoestrogen
concentration, distribution of different oestrogen receptor types9 and ethnicity10. The
suggested mechanism of action is as shown below.
Figure 1
Since endogenous oestrogen is widely recognized as a risk factor for breast cancer2,5, the
antagonistic actions of phytoestrogens may reduce the chances of developing the disease8.
However, other studies have shown that phytoestrogens display modest agonistic activity in
low concentrations of endogenous oestrogens, which might promote breast cancer cell
proliferation11.
What do we intend to do?
With numerous studies yielding mixed results, our group aims to evaluate if present evidence
regarding the effects of phytoestrogen consumption on the development of breast cancer is
sufficient to conclude whether phytoestrogens are truly friends or foes where breast cancer is
concerned.
What will we be looking at?
These are the markers that we will look at to assess breast cancer risk:
Mammographic density
Several studies have consistently associated high mammographic density with increased
breast cancer risk12,13. The underlying mechanism is still unclear but it has been hypothesised
that breast density indicates hormonal and reproductive events that could modulate breast
cancer risk14.
Blood oestradiol levels
High levels of serum oestradiol is strongly-linked to elevated breast cancer risk, particularly
in postmenopausal women15,16. Concerning premenopausal women, data from prospective
studies is limited but suggest similar associations15. These effects could be due to stimulation
of increased rate of mitosis in breast epithelial cells17,18,19.
BRCA1 and BRCA2 mRNA levels
BRCA1 and BRCA2 are tumour suppressor genes that are expressed extensively in tumour
cells in response to DNA damage20,21. They play a crucial role in mammary epithelial cell
growth regulation20, particularly in the maintenance of genomic integrity and transcriptional
regulation22.
Sister chromatid exchange(SCE)
SCE indicates DNA instability23,24. Breast cancer patients have shown a higher mean value of
SCE compared to controls25,26.
MECHANISMS
Many modes of action have been proposed for explaining how phytoestrogens affect an
individual’s risk of developing breast cancer, as well as the prognosis of breast cancer
patients. A few of these are outlined below:
Action at oestrogen receptors
Phytoestrogens bind to oestrogen receptors, where they act like selective oestrogen receptor
modulators, in a similar way to the breast cancer drug tamoxifen 27. Phytoestrogens have a
higher binding affinity for ERβ receptors than ERα receptors, and, in breast tumour cells,
genes upregulated by ERβ generally supress proliferation. Therefore, phytoestrogens may
reduce tumour growth by increasing the expression of genes that reduce tumour cell
proliferation28.
Changes in circulating oestrogen
Phytoestrogens can change the level of circulating endogenous oestrogen by both reducing
the synthesis of oestrogen and reducing its transport in the blood. Some phytoestrogens
disrupt enzymes involved in steroid hormone biosynthesis, reducing the amount of oestrogen
produced. Some phytoestrogens can bind to sex hormone binding globulin (SHBG), which is
the molecule that oestrogen is bound to when it is in the blood. By binding to SHBG,
phytoestrogens can displace oestrogen, and therefore slightly reduce circulating oestrogen. As
oestrogen is known to increase tumour cell proliferation, a change in blood oestrogen level
will influence an individual’s risk of breast cancer28.
Inhibition of the synthesis of oestrogen in breast tissue
Oestrogen can be synthesised in extragonadal tissues, including breast tissue, from steroid
precursors found in the blood. Indeed, in postmenopausal women, all their oestrogen is
formed in extragonadal tissues. One enzyme key to this conversion is aromatase, which is
inhibited by some phytoestrogens, such as flavones. As high levels of oestrogen synthesis in
breast tissue is closely linked with breast cancer, a reduction in extragonadal tissue synthesis
of oestrogen by phytoestrogens could help protect against breast cancer29.
Regulation of mediators involved in cell growth and proliferation
Certain phytoestrogens inhibit protein tyrosine kinases (PTKs) in breast cancer cells; PTKs
activate intracellular proteins, including growth factors required in tumour cell proliferation,
and therefore phytoestrogens may also reduce tumour growth by this mechanism.
Phytoestrogens also regulate the expression of other mediators involved in tumour growth,
for example genistein down-regulates vascular endothelial growth factor which is needed for
tumours to grow and metastasise28.
METHODS
Protocol
The mini-summary adopted the format suggested by the PRISMA guidelines30,which laid out
how to carry out various systematic reviews and meta-analyses. When critically reviewing
papers, we used the basic format suggested in the study guide.
Information sources
The first searches we did into phytoestrogens were based on two systematic reviews 28,31. We
used the information derived from these as a starting point for google searches into the effects
of phytoestrogens on various body systems. Alongside this, we began the screening process
for potential papers to be included in the summary. After deciding to focus on breast cancer,
we started our literature search.
Literature searches
Two medical paper databases were used to search for papers. On Medline/Ovid the searched
terms “phytoestrogens” and “breast neoplasms” were applied, which were further limited to
“humans” and “clinical trials” only. Parallel terms and limits were used on PubMed. After
removing duplicates and inaccessible papers, we added the remaining to a literature search
table under condensed headings: year of publication, title, author, journal, study type, study
population, type of phytoestrogen investigated, length of study, results and conclusions.
Study selection
From the thirty papers that were submitted to the literature search table, eight were included
in the final data extraction table after fulfilling our eligibility criteria. These were randomised
control trials whose outcomes related specifically to breast cancer prevention with clinical
outcomes and were accessible to us online.
Data collection process
The included articles which passed the eligibility criteria were submitted to a data extraction
table under additional headings, which comprised of: risk of bias, outcome measures,
diagnostic criteria, missing or excluded participants, and strengths and weaknesses of the
studies.
Data items
In line with our aims, we chose to compare some commonly used markers for breast cancer:
percentage change in mammographic breast density32, change in blood oestrodiol levels33,34,35,
change in BRCA1&2 mRNA levels21,22 and the change in sister chromatid exchange36.
Risk of bias in individual studies
Criteria from the Cochrane handbook37 were used to assess different aspects of risk of bias
including: randomization, blinding, completeness of data and selective reporting. As none of
the studies chosen had a particularly high risk of bias overall, no papers were excluded on
this basis.
Primary summary measures
The tests used to analyse the data were regular and fixed means, standard deviations and 95%
confidence intervals for the odds ratios obtained for the risk of breast cancer (between the
phytoestrogen intervention and placebo groups), for pre and postmenopausal women.
Synthesis of results
Statistical analyses were done using Review Manager 5.338software as recommended by the
Cochrane Handbook for Systematic Reviews of Interventions37.For percentage change in
mammographic breast density, the results of three studies39,40,41were analysed using a Forrest
plot to assess the overall effect of phytoestrogens on pre- and postmenopausal women both
separately and together. Since different measures were used to evaluate percentage change in
mammographic breast density, three of the studies42,43,44 had their outcomes assessed individually.
For change in blood oestradiol levels, the results from the three studies that investigated this
outcome39,45,46 were analysed individually due to inconsistent measures across the studies. For
change in BRCA1&2 mRNA levels and sister chromatid exchange (SCE), results from the
one study43 were assessed individually as this was the only study found that investigated this
outcome
All included studies were critically analysed to assess the quality of evidence provided, based
on the GRADE working group’s grades of evidence, as recommended by the Cochrane
Handbook for Systematic Reviews of Interventions37.
Chi-squared and the I2 test were used to test for the heterogeneity of the results between
studies (whether the percentage variation between the studies was down to their heterogeneity
or chance), with given p-values. Z values (standard scores) were used to analyse the spread
of data around the population mean, also with given p-values.
Risk of bias across studies
We assessed the risk of bias at study level across the papers, using criteria and the risk of bias
at outcome level from the Cochrane handbook37, which were presented in graphical form
using RevMan software38, which enabled us to compare the results.
No additional analysis was performed.
RESULTS
Study Characteristics
Table 1 summarises the key features of each paper from which the results were obtained.
Table 1
Our results compared percentage change in mammographic breast density32, change in blood
oestrodiol levels33,34,35, change in BRCA1&2 mRNA levels21,22 and the change in sister
chromatid exchange36.
Percentage change in mammographic breast density
The sizes of the green squares in figure 2 represent the weight given to individual papers
based on sample size and hence statistical power. The diamonds are indicators of overall
effect of phytoestrogens compared to placebo; where a line connecting the top and bottom
vertices marks the value for mean difference between the two groups, and a line connecting
the lateral vertices marks the confidence interval range.
Figure 2
In pre-menopausal women, results show that phytoestrogens significantly increased breast
mammographic density( mean difference=3.04; 95% CI 0.29 to 5.79; P=0.03). In postmenopausal women, results show no significant differences between phytoestrogen and
placebo groups. ( mean difference=0.77; 95% CI -2.44 to 3.97; P=0.64)
Overall, there were no significant differences between premenopausal and postmenopausal
women(P=0.29)
Meta-analysis for three studies39,40,41, show that there is no strong evidence to show that
phytoestrogens have an effect on mammographic breast density(Mean Difference= 2.08; 95%
CI -0.01 to 4.16; P=0.05). Three studies were excluded42,43,44 from meta-analysis due to
different measures of evaluating outcome.
All showed no significant difference between phytoestrogen and placebo groups in
postmenopausal women except for one44, where Wolfe classification showed significant
reduction in mammographic density for the phytoestrogen group.
Change in blood oestradiol levels
Three studies showed no significant differences between phytoestrogen and placebo groups
in both premenopausal women45and postmenopausal women.39,46
Change in BRCA1 and BRCA2 mRNA levels
One study44 showed that the phytoestrogen group had significantly higher BRCA1 and BRCA2
mRNA levels compared to the placebo group after two and three years of treatment (P<0.001), with a
treatment x time interaction also being significant (P<0.0001). It was also reported that there was no
significant change in BRCA1 and BRCA2 mRNA levels at all within the phytoestrogen group,
although P-values comparing the levels after two and three years of treatment were not stated. The
placebo group showed a significant decrease in BRCA1 and BRCA2 mRNA levels compared to the
baseline values (P<0.001) after three years of treatment. These findings suggest that BRCA1 and
BRCA2 mRNA levels were maintained in the phytoestrogen group compared to the placebo group.
Change in sister chromatid exchange (SCE)
One study44 on postmenopausal women showed a significant decrease in SCE in the
phytoestrogen group (P<0.001). The change was proven to be greater over time (P<0.0001).
Risk of bias
Summary of bias in each individual study
Figure 3
Assessment of bias across all studies
Figure 4
The summary of risk of bias in each individual study can be found in Figure 3. All papers
showed a low risk of selection bias in random sequence generation, and none of them had
more than two sections that exhibit a high risk of bias. The most common sources of bias
were incomplete outcome data and the exclusion of women on HRT (which is accounted for
under “other bias”). Only one paper42 had a low risk of bias for all sections.
Quality of Evidence
Table 2
DISCUSSION
Our results
Our analysis of the papers we collected focused on four measures for breast cancer risk:
mammographic density, blood oestradiol levels, BRCA1 and BRCA2 mRNA expression, and
sister chromatid exchange.
For three indicators (changes in mammographic density, blood oestradiol levels and BRCA1
and BRCA2 mRNA expression) there was no significant difference between the groups
receiving phytoestrogens and the placebo in postmenopausal women. In premenopausal
women, an adverse effect of phytoestrogen treatment was observed as there was a significant
increase in mammographic breast density in the phytoestrogen group compared to placebo.
However, as only one study of high quality of evidence showed this result, definitive
conclusions cannot be drawn from it.
The final measure, changes in sister chromatid exchange (SCE), was only investigated in one
study43, which showed a significant decrease in SCE in the phytoestrogen group compared to
the placebo group (P<0.001). As SCE is a risk factor for breast cancer36, the decrease in SCE
would suggest that phytoestrogens may have a protective role against breast cancer.
However, this was only observed in one study, and is not sufficient to conclude whether
phytoestrogens do indeed alter an individual’s risk of developing breast cancer.
Problems with drawing conclusions from these studies
The studies we included in our analysis looked at phytoestrogens in supplement form,
whereas most people’s intake of phytoestrogens comes from food consumption28, in particular
products such as soy, flax seeds and many vegetables28. These foods will contain other
substances in addition to phytoestrogens that may influence phytoestrogen uptake and
metabolism by the body28. Therefore, phytoestrogen supplements may not have the same
effect on breast cancer risk as phytoestrogen containing foods. In addition, different
supplements contain different types and doses of phytoestrogens, so the effects observed in
these studies may not be seen with all supplements, especially if the effect is dose dependent.
Not everyone will respond the same to phytoestrogens; differences in gut microbiota may
affect isoflavone availability for example by conjugating them into more bioactive forms31.
Also, phytoestrogens may exert their effect at many different receptor sites across the body
that are expressed to a different extent between individuals31. Therefore, even if breast cancer
risk across the populations in our studies as whole did not seem to change, this may not
necessarily be true for each individual.
It has been suggested that phytoestrogens may have the biggest impact on breast cancer risk
when exposure occurs before puberty, or even before birth28. Currently, however, there are no
RCTs that investigate the effect of phytoestrogen consumption at this age, potentially because
of the ethical issues involved in using children in clinical trials.
Another problem with drawing conclusions about the risk of breast cancer with phytoestrogen
consumption is that there simply is not enough evidence to establish a causal link. In
addition, publication bias may be a factor as inconclusive or negative results may not be
published in favour of more positive outcomes.
Finally, the RCTs are limited in the time period they cover – even the longest trials are only
about two years in length, and so may not be able to detect a change in risk that occurs after
decades of consumption of phytoestrogens. Thus, a small change in risk over two years could
be magnified to a significant change in risk over a lifetime.
Future research
In the UK, breast cancer is the most common cancer, with 49,936 women diagnosed in 2011,
and is third highest cause of death47. Given that diet is a major component in everyone’s life,
comprehensive research concerning consumption of phytoestrogens and breast cancer risk
has the potential to save many lives. However, currently the evidence is insufficient to draw a
meaningful conclusion, and as such we believe that more trials need to be carried out with
larger sample sizes, in order to acquire the necessary evidence to provide sound advice to
people regarding their consumption of phytoestrogen-containing supplements or foods.
One of the disadvantages of RCTs investigating cancer risk in relation to diet is that it takes
many years to produce definitive results. However, advances such as microarray technologies
can measure changes in biomarkers, such as gene expression or protein production, which
can provide information on cancer risk in a much shorter period of time. Therefore, we
believe that this a promising advancement and an area that could be explored in future trials.
CONCLUSIONS
There is currently insufficient evidence to provide reliable public health information
concerning the consumption of phytoestrogens and breast cancer risk. However, it is
important to recognise that phytoestrogens are not the only potentially beneficial substance in
isoflavone containing foods, for example soy, seeds and certain vegetables, which may have
many other health benefits.
Phytoestrogens are also being investigated for their potential benefits in protecting against
cardiovascular disease and osteoporosis, and for alleviating the symptoms of
menopause. Therefore, their effects on breast cancer should be considered alongside these
when determining whether or not they should be increased in people’s diets.
REFLECTIONS
Our group chose this SSC for a variety of reasons. Some of us had never encountered the
subject of phytoestrogens before and were curious to find out more, whilst others were
interested by the frequency in which phytoestrogens in relation to health problems appear in
the media.
Due to phytoestrogens being such a broad subject, at the beginning of our research we were
unsure of where to focus. We initially looked at phytoestrogens and their effects on several
different body systems before deciding to focus on cancer due to the severity of the issue and
its impact on many lives. We then narrowed the focus further to breast cancer as there was
extensive literature available for us to analyse. Clarifying the aim of our SSC project enabled
us to quickly progress in our research and literature searching. We were all very interested in
the idea that phytoestrogens could reduce the risk of developing breast cancer and that future
research in this area would be incredibly useful.
Throughout the SSC project our team worked well together and were consistently efficient.
We divided tasks evenly and fairly to utilise individual strengths. Everyone has improved
personal skills such as teamwork and communication, as well as increasing knowledge
surrounding breast cancer and mechanisms and effects of phytoestrogens.
CONTRIBUTIONS
All members of the group proofread the others’ work and contributed to the final version of
all text on the site.
Lee Pei Si (Sophia)
Sophia co-wrote the introduction, co-wrote results in particular the bias section and did the
initial draft of the critical appraisal.
Esther McNeill
Esther co-wrote the results section in particular the study characteristics table.
Lucy Nevin
Lucy co-designed the website i.e. its format, co-wrote the methods section and compiled the
references.
Charlotte Pattison
Charlotte co-wrote the discussion section and was the primary author of the reflections.
Arjunan Selvamani
Arjunan co-wrote the introduction and results sections and in particular focused on synthesis
of results through statistical analysis.
Andrew Whitelaw
Andrew co-designed the website, wrote the information search report and co-wrote the methods
section.
Jess Woods
Jess co-wrote the discussion section and wrote the mechanisms section.
CRITICAL APPRAISAL
Group Critical Appraisal
Soy protein Containing Isoflavones and Mammographic Density in a Randomised
Controlled Trial in Postmenopausal Women byVerheus et al., 2008
Aims and Objectives
To determine the effect of one year soy supplementation on mammographic density among
post-menopausal women
Population
Dutch post-menopausal women aged 60-75 years.
Study design
Randomised controlled trial
Size of study
126 women (56 in placebo and 70 in soy group) – Excluded women who were current or
previous users of Hormone Replacement Therapy, or had a history or presence of
malignancy.
Intervention
Intervention group participants received 36.5 g of soy powder containing 99 mg isoflavones
daily (52 mg genistein, 41 mg daidzein, and 6 mg glycitein). Those in placebo group received
36.5 g of milk protein with identical taste and appearance for one year.
Randomisation process
A list of randomisation numbers was computer-generated by personnel not involved in the
trial. Subjects were assigned randomisation numbers, corresponding with one of the two
possible interventions, in order of enrolment into the trial. Mammograms were assessed by
one observer in sets of randomly ordered films.
Blinding
Double-blinded study. Supplement boxes were fixed with adhesives with randomisation
numbers. There was no chance of unblinding when distributing supplies.
Statistical tests
Data was analysed using the Statistical Analysis System software package, release 9.1 (SAS
Institute). P-values were used to compare differences between both groups. Two-sided P
values of <0.05 were considered statistically significant.
Outcome measure
Mammographic density was calculated using total breast area and area of dense tissue within
breast using a computer-assisted method on mammographs. TR-FIA kits (Labmaster) were
used to measure equol concentrations which determined metabolism status.
Main results
Both study groups showed no significant differences in the decrease in absolute
mammographic density (-1.09 cm², P=0.42) and percent density (-0.44%, P=0.78). The
observed decrease in these outcomes was most likely a natural involution of breast with age.
Equol-producing status did not affect the results (difference in percent density between
intervention and placebo group for equol producers and non-producers were -0.00 and -0.01
respectively; P = 0.95).
Sources of Bias




Selection bias: Low risk as patients were randomly allocated.
Performance bias: Low risk as study was double-blind.
Observation bias: No specific mention of blinding of the observer who assessed the
mammograms.
Attrition bias: Incomplete outcome data as many women had less than two mammograms
retrievable (20/87 from placebo, 11/88 from intervention group).
Comments
Strengths
 Long duration of study allowed sufficient time for changes to be observed.
 Large amount of soy protein consumed (in the upper range of dietary intake in Asian
countries)
 Participant’s compliance was assessed and was good.
 Assessed participant’s ability to produce equol, potentially defining which participants
benefit most from soy consumption.
 No inter-observer variability as only one observer was employed.
Weaknesses
 Unequal time delay between end of trial and post-trial mammography. Possible effect of
treatment may have diminished by then.


Wide confidence intervals in results suggest that study was underpowered, which was due
to failure of obtaining post-trial mammographs from women over 75 years old.
Multivariate statistical analysis not performed to control for potential confounding factors
like age, BMI and smoking status.
Conclusion
As a group, we felt that this study was generally well designed as it analysed factors proposed
to affect the action of phytoestrogens such as one’s equol-producing status and the high
intake of soy protein observed in Asian countries. Study findings did not support any effect of
phytoestrogens on breast cancer risk. However, it may not be truly representative of the
general population as the sample size was relatively small and many women were excluded
from the study. Therefore, we believe a greater sample size is required to improve its validity.
Word count: 599 words (excluding title)
DATA EXTRACTION TABLE
Please click for Data Extraction Table.
ELIGIBILITY CRITERIA
(click diagram to enlarge)
INFORMATION SEARCH REPORT
Recognising the information gap
We gained an overview of the topic using the first two systematic reviews 28,31 we were sent
by our tutor. These developed our knowledge of the mechanisms of the effects
phytoestrogens had in major body systems, and acted as a starting point for further reading.
We supplemented this with database searches for papers looking into the effects of
phytoestrogens.
Distinguishing ways to address this
After deciding we wanted to focus on the effects on cancer, cardiovascular and menopause,
we split ourselves up between these areas, and used the databases Medline and PubMed to
find related articles, as these had provided many relevant papers in prior searches. We mainly
looked for systematic reviews and a few clinical trials, to gain an understanding of the
specific effects in these systems. This led us to the decision to focus on breast cancer, as this
topic had the largest body of research.
Constructing strategies to find the information
We chose to use the similar search terms (“breast neoplasms” AND “phytoestrogens”,
combined with the Boolean logic term AND) on both Medline and PubMed to find papers.
Medline offered a higher degree of result filtering than PubMed, hence we limited the
searches on PubMed to “trials” and limited those on Medline to “human trials” and
“randomised control trials”. We also cross-referenced these papers to ensure that we hadn’t
missed out any key trials done into the subject.
Locating and accessing the information
We could access all the papers we found this way through the university findit@edinbugh
service.
LITERATURE SEARCH TABLE
Please click for Literature Search Table
REFERENCES
Introduction and Mechanisms
(Unless stated, the information taken from the following review articles, websites and
primary research articles cited below was taken from abstracts and small sections of the
text.)
1. Cathy Wong. The Benefits of Phytoestrogens. http://altmedicine.about.com/od/completeaz
index/a/phytoestrogens.htm (accessed 9 October 2014) (website)
2. Ziegler RG. Phytoestrogens and breast cancer. The American Journal of Clinical Nutrition.
2004;79(2):183-4. (review article)
3. National Women’s Health Network. Herbs and Phytoestrogens. https://nwhn.org/herbsand-phytoestrogens (accessed 11 October 2014) (website)
4. Davis SR. Phytoestrogen therapy for menopausal symptoms. British Medical Journal.
2001;323(7309):354-5. (review article)
5. Usui T. Pharmaceutical Prospects of Phytoestrogens. Endocrine Journal. 2006;53(1): 7-20.
(review article)
6. World Health Organisation – International Agency for Research on Cancer. The Global
Cancer Atlas. 2012. (WHO publication)
7. Ward HA, Kuhnle GG. Phytoestrogen consumption and association with breast, prostate
and colorectal cancer in EPIC Norfolk. Archives of Biochemistry and Biophysics.
2010;501(1):170-5. (review article)
8. Leclercq G, Jacquot Y. Interactions of isoflavones and other plant derived estrogens with
estrogen receptors for prevention and treatment of breast cancer—Considerations concerning
related efficacy and safety. Journal of Steroid Biochemistry & Molecular Biology.
2014;139:237-44. (review article)
9. Cassileth BR, Yarett I. American Society of Clinical Oncology (ASCO). Soy
Phytoestrogens and Breast Cancer: An Enduring Dilemma.
http://www.ascopost.com/issues/july-15-2012/soy-phytoestrogens-and-breast-cancer-anenduring-dilemma.aspx (accessed 17 Oct 2014) (website)
10. Keinan-Boker L, Der Schouw YT, Grobbee DE, Peeters PHM. Dietary phytoestrogens
and breast cancer risk. The American Journal of Clinical Nutrition. 2004;79(2):282-8.
(review article)
11. Stacey M. The Effects of Phytoestrogens on Hot Flashes. Nutrition Bytes. 2003;9(2).
(review article)
12. McCormack V. Breast Density and Parenchymal Patterns as Markers of Breast Cancer
Risk: A Meta-analysis. Cancer Epidemiology Biomarkers & Prevention. 2006;15(6):11591169. (meta-analysis)
13. Boyd NF, Lockwood GA, Byng JW, Tritchler DL, Yaffe MJ. Mammographic Densities
and Breast Cancer Risk. Cancer Epidemiology, Biomarkers & Prevention. 1998;7(12):113344. (review article)
14. American Cancer Society. Breast density and your mammogram report.
http://www.cancer .org/breast-density-and-your-mammogram-report (accessed 15 November
2014) (website)
15. Key TJ. Serum oestradiol and breast cancer risk. Endocrine-Related Cancer.
1999;6(2):175-80. (review article)
16. Zhang X, Tworoger SS, Eliassen AH, Hankinson SE. Postmenopausal plasma sex
hormone levels and breast cancer risk over 20 years of follow-up. Breast Cancer Research
and Treatment. 2013;137(3): 883-92. (primary research article)
17. Cohen SM, Ellwein LB. Cell proliferation in carcinogenesis. Science. 1990;249:1007-11.
(online article)
18. Pike MC, Spicer DV, Dahmoush L, Press MF. Estrogens, progestogens, normal breast
cell proliferation, and breast cancer risk. Epidemiologic Reviews. 1993;15:17-35. (review
article)
19. Preston-Martin S, Pike MC, Ross RK, Jones PA, Henderson BE. Increased cell division
as a cause of human cancer. Cancer Research. 1990;50:7415-71. (review article)
20. Chodosh LA. Expression of BRCA1 and BRCA2 in Normal and Neoplastic Cells.
Journal of Mammary Gland Biology and Neoplasia. 1998;3(4): 389-402. (review article)
21. National Cancer Institute. BRCA1 and BRCA2: Cancer Risk and Genetic Testing.
http://www.cancer.gov/cancertopics/factsheet/Risk/BRCA (accessed 15 November 2014)
(website)
22. Welcsh PL, King M. BRCA1 and BRCA2 and the genetics of breast and ovarian cancer.
Human Molecular Genetics. 2001;10(7):705 -13. (review article)
23. Perry P, Evans HJ. Cytological detection of mutagen-carcinogen exposure by sister
chromatid exchange. Nature. 1975;258(5531):121-5. (primary research article)
24. Carrano AV, Thompson LH, Lindl PA, Minkler JL. Sister chromatid exchange as an
indicator of mutagenesis. Nature. 1978;271: 551-3. (primary research article)
25. Dhillon VS, Bhasker R, Kler RS, Husain SA. Sister Chromatic Exchange (SCE) Studies
in Breast Cancer Patients: A Follow-Up Study. Cancer Genetics and Cytogenetics.
1995;80(2):115-7. (primary research article)
26. Husain SA, Balasubramanian S, Bamezai R. Sister Chromatid Exchange Frequency in
Breast Cancer Cases. Cancer Genetics and Cytogenetics. 1992;61(2):142-6. (primary research
article)
27. Oseni T, Patel R, Pyle J, Jordan V. Selective Estrogen Receptor Modulators and
Phytoestrogens. Planta Med. 2008;74(13):1656-1665. (review article)
28. Patisaul H, Jefferson W. The pros and cons of phytoestrogens. Frontiers in
Neuroendocrinology. 2010;31(4):400-419. (review article read in full by all members of
group)
29. Rice S, Whitehead S. Phytoestrogens and breast cancer -promoters or protectors?.
Endocrine Related Cancer. 2006;13(4):995-1015. (review article)
Methods, Results and Discussion
(Unless stated, the information taken from the following review articles, websites and
primary research articles cited below was taken from abstracts and small sections of the
text.)
30. Moher D, Liberati A, Tetzlaff J, Altman D. Preferred reporting items for systematic
reviews and meta-analyses: the PRISMA statement. BMJ. 2009;339(jul21 1):b2535-b2535.
(handbook/checklist accessed through BMJ, read thoroughly by several members of the
group)
31. Sirotkin A, Harrath A. Phytoestrogens and their effects. European Journal of
Pharmacology. 2014;741:230-236. (review article read in full by all members of the
group)
32. Vachon C, van Gils C, Sellers T, Ghosh K, Pruthi S, Brandt K et al. Mammographic
density, breast cancer risk and risk prediction. Breast Cancer Research. 2007;9(6):217.
(review article)
33. Hankinson S, Willett W, Manson J, Colditz G, Hunter D, Spiegelman D et al. Plasma Sex
Steroid Hormone Levels and Risk of Breast Cancer in Postmenopausal Women. JNCI Journal
of the National Cancer Institute. 1998;90(17):1292-1299. (primary research article)
34. Key TJ, Appleby PN, Reeves GK, et al. for the Endogenous Hormones and Breast Cancer
Collaborative Group. Circulating sex hormones and breast cancer risk factors in
postmenopausal women: reanalysis of 13 studies. Br J Cancer. 2011;105(5):709-22,
(secondary research article)
35. Cauley J. Elevated Serum Estradiol and Testosterone Concentrations Are Associated with
a High Risk for Breast Cancer. Annals of Internal Medicine. 1999;130(4):270. (primary
research article)
36. Safinejad K, Mahdieh M, Mahdipour P, Yadegar L, Atri M, Javadi G. Sister chromatid
exchange in peripheral blood lymphocytes as a possible breast cancer risk biomarker: A study
of Iranian patients with breast cancer. Egypt J Med Hum Genet. 2009;10(1):55-61. (primary
research article)
37. Higgins J, Green S. Cochrane handbook for systematic reviews of interventions.
Chichester, England: Wiley-Blackwell; 2008.(handbook read in depth by several members
of the group)
38. cochrane.org. RevMan | Informatics & Knowledge Management Department [Internet].
2014 [cited 16 November 2014]. Available from: http://tech.cochrane.org/revman (software
used for results analysis)
39. Atkinson C, Warren R, Sala E, Bingham S, Dowsett M, Dunning A et al. Red-cloverderived isoflavones and mammographic breast density: a double-blind, randomized, placebocontrolled trial. Breast Cancer Research. 2004;6(3):R170-R179. (primary research paper read
fully and analysed in detail)
40. Powles T, Howell A, Evans D, McCloskey E, Ashley S, Greenhalgh R et al. Red clover
isoflavones are safe and well tolerated in women with a family history of breast cancer.
Menopause International. 2008;14(1):6-12. (primary research paper read fully and analysed
in detail)
41. Maskarinec G, Williams A, Carlin L. Mammographic densities in a one-year isoflavone
intervention. European Journal of Cancer Prevention. 2003;12(2):165-169. (primary research
paper read fully and analysed in detail)
42. Delmanto A, Nahas-Neto J, Traiman P, Uemura G, Pessoa E, Nahas E. Effects of soy
isoflavones on mammographic density and breast parenchyma in postmenopausal women.
Menopause. 2013;20(10):1049-1054. (primary research paper read fully and analysed in
detail)
43. Verheus M, van Gils C, Kreijkamp-Kaspers S, Kok L, Peeters P, Grobbee D et al. Soy
Protein Containing Isoflavones and Mammographic Density in a Randomized Controlled
Trial in Postmenopausal Women. Cancer Epidemiology Biomarkers & Prevention.
2008;17(10):2632-2638. (primary research paper read fully and analysed in detail)
44. Marini H, Bitto A, Altavilla D, Burnett B, Polito F, Di Stefano V et al. Breast Safety and
Efficacy of Genistein Aglycone for Postmenopausal Bone Loss: A Follow-Up Study. The
Journal of Clinical Endocrinology & Metabolism. 2008;93(12):4787-4796. (primary research
paper read fully and analysed in detail)
45. Kumar N, Cantor A, Allen K, Riccardi D, Cox C. The specific role of isoflavones on
estrogen metabolism in premenopausal women. Cancer. 2002;94(4):1166-1174. (primary
research paper read fully and analysed in detail)
46. Steinberg F, Murray M, Lewis R, Cramer M, Amato P, Young R et al. Clinical outcomes
of a 2-y soy isoflavone supplementation in menopausal women. American Journal of Clinical
Nutrition. 2010;93(2):356-367. (primary research paper read fully and analysed in detail)
47. org. Breast cancer statistics : Cancer Research UK [Internet]. 2014 [cited 22 November
2014]. Available from: http://www.cancerresearchuk.org/cancerinfo/cancerstats/types/breast/?script=true (website)
Studies included in Data extraction table
(The studies below are primary research articles which were read fully and analysed in
detail)
39. Atkinson C, Warren R, Sala E, Bingham S, Dowsett M, Dunning A et al. Red-cloverderived isoflavones and mammographic breast density: a double-blind, randomized, placebocontrolled trial. Breast Cancer Research. 2004;6(3):R170-R179.
40. Powles T, Howell A, Evans D, McCloskey E, Ashley S, Greenhalgh R et al. Red clover
isoflavones are safe and well tolerated in women with a family history of breast cancer.
Menopause International. 2008;14(1):6-12.
41. Maskarinec G, Williams A, Carlin L. Mammographic densities in a one-year isoflavone
intervention. European Journal of Cancer Prevention. 2003;12(2):165-169.
42. Delmanto A, Nahas-Neto J, Traiman P, Uemura G, Pessoa E, Nahas E. Effects of soy
isoflavones on mammographic density and breast parenchyma in postmenopausal women.
Menopause. 2013;20(10):1049-1054.
43. Verheus M, van Gils C, Kreijkamp-Kaspers S, Kok L, Peeters P, Grobbee D et al. Soy
Protein Containing Isoflavones and Mammographic Density in a Randomized Controlled
Trial in Postmenopausal Women. Cancer Epidemiology Biomarkers & Prevention.
2008;17(10):2632-2638.
44. Marini H, Bitto A, Altavilla D, Burnett B, Polito F, Di Stefano V et al. Breast Safety and
Efficacy of Genistein Aglycone for Postmenopausal Bone Loss: A Follow-Up Study. The
Journal of Clinical Endocrinology & Metabolism. 2008;93(12):4787-4796.
45. Kumar N, Cantor A, Allen K, Riccardi D, Cox C. The specific role of isoflavones on
estrogen metabolism in premenopausal women. Cancer. 2002;94(4):1166-1174.
46. Steinberg F, Murray M, Lewis R, Cramer M, Amato P, Young R et al. Clinical outcomes
of a 2-y soy isoflavone supplementation in menopausal women. American Journal of Clinical
Nutrition. 2010;93(2):356-367.
Studies included in literature search table but excluded from data extraction table
(The studies below are primary research articles of which generally only the abstracts were
read )
48. Xu X, Duncan A, Wangen K, Kurzer M. Soy consumption alters endogenous estrogen
metabolism in postmenopausal women. Cancer Epidemiology Biomarkers & Prevention.
2000;9(8):781-786.
49. Quella S, Loprinzi C, Barton D, Knost J, Sloan J, LaVasseur B et al. Evaluation of soy
phytoestrogens for the treatment of hot flashes in breast cancer survivors: A North Central
Cancer Treatment Group Trial. Journal of Clinical Oncology. 2000;18(5):1068-1068.
50. Brown B, Thomas W, Hutchins A, Martini M, Slavin J. Types of dietary fat and soy
minimally affect hormones and biomarkers associated with breast cancer risk in
premenopausal women. Nutrition and cancer. 2002;43(1):22-30.
51. Van Patten C, Olivotto I, Chambers G, Gelmon K, Hislop T, Templeton E et al. Effect of
soy phytoestrogens on hot flashes in postmenopausal women with breast cancer: a
randomized, controlled clinical trial. Journal of Clinical oncology. 2002;20(6):1449-1455.
52. Nikander E, Metsä-Heikkilä M, Tiitinen A, Ylikorkala O. Evidence of a Lack of Effect of
a Phytoestrogen Regimen on the Levels of C-Reactive Protein, E-Selectin, and Nitrate in
Postmenopausal Women. The Journal of Clinical Endocrinology & Metabolism.
2003;88(11):5180-5185.
53. Dai Q, Franke AA, Yu H, Shu XO, Jin F, Hebert JR, Custer LJ, Gao YT, Zheng W.
Urinary phytoestrogen excretion and breast cancer risk: evaluating potential effect modifiers
endogenous estrogens and anthropometrics. Cancer Epidemiology, Biomarkers & Prevention.
2003;12(6):497-502.
54. Nikander E. A randomized placebo-controlled crossover trial with phytoestrogens in
treatment of menopause in breast cancer patients. Obstetrics & Gynecology.
2003;101(6):1213-1220.
55. Bonorden M, Greany K, Wangen K, Phipps W, Feirtag J, Adlercreutz H et al.
Consumption of Lactobacillus acidophilus and Bifidobacterium longum do not alter urinary
equol excretion and plasma reproductive hormones in premenopausal women. Eur J Clin
Nutr. 2004;58(12):1635-1642.
56. Nettleton JA, Greany KA, Thomas W, Wangen KE, Adlercreutz H, Kurzer MS. Plasma
phytoestrogens are not altered by probiotic consumption in postmenopausal women with and
without a history of breast cancer. Journal of Nutrition. 2004;134(8):1998-2003.
57. Nikander E, Metsä-Heikkilä M, Ylikorkala O, Tiitinen A. Effects of Phytoestrogens on
Bone Turnover in Postmenopausal Women with a History of Breast Cancer. The Journal of
Clinical Endocrinology & Metabolism. 2004;89(3):1207-1212.
58. Nhan S, Anderson K, Nagamani M, Grady J, Lu L. Effect of a Soymilk Supplement
Containing Isoflavones on Urinary F2 Isoprostane Levels in Premenopausal Women.
Nutrition and Cancer. 2005;53(1):73-81.
59. Nettleton J, Greany K, Thomas W, Wangen K, Adlercreutz H, Kurzer M. Short-Term Soy
and Probiotic Supplementation Does Not Markedly Affect Concentrations of Reproductive
Hormones in Postmenopausal Women with and Without Histories of Breast Cancer. The
Journal of Alternative and Complementary Medicine. 2005;11(6):1067-1074.
60. Lukaczer D, Darland G, Tripp M, Liska D, Lerman RH, Schiltz B, Bland JS. Clinical
effects of a proprietary combination isoflavone nutritional supplement in menopausal women:
a pilot trial. Alternative Therapies in Health & Medicine. 2005;11(5):60-5.
61. Nettleton JA, Greany KA, Thomas W, Wangen KE, Adlercreutz H, Kurzer MS. The
Effect of Soy Consumption on the Urinary 2:16-Hydroxyestrone Ratio in Postmenopausal
Women Depends on Equol Production Status but Is Not Influenced by Probiotic
Consumption. Journal of Nutrition. 2005;135(3):603-8.
62. Yang S, Zhou Q, Yang X. Caspase-3 status is a determinant of the differential responses
to genistein between MDA-MB-231 and MCF-7 breast cancer cells. Biochimica et
Biophysica Acta (BBA) – Molecular Cell Research. 2007;1773(6):903-911.
63. Setchell K, Brown N, Zhao X, Lindley S, Heubi J, King E et al. Soy isoflavone phase II
metabolism differs between rodents and humans: implications for the effect on breast cancer
risk. American Journal of Clinical Nutrition. 2011;94(5):1284-1294.
64. Zaineddin A, Buck K, Vrieling A, Heinz J, Flesch-Janys D, Linseisen J et al. The
Association Between Dietary Lignans, Phytoestrogen-Rich Foods, and Fiber Intake and
Postmenopausal Breast Cancer Risk: A German Case-Control Study. Nutrition and Cancer.
2012;64(5):652-665.
65. Swann R, Perkins K, Velentzis L, Ciria C, Dutton S, Mulligan A et al. The DietCompLyf
study: A prospective cohort study of breast cancer survival and phytoestrogen consumption.
Maturitas. 2013;75(3):232-240.
66. MacGregor C, Canney P, Patterson G, McDonald R, Paul J. A randomised double-blind
controlled trial of oral soy supplements versus placebo for treatment of menopausal
symptoms in patients with early breast cancer. European Journal of Cancer. 2005;41(5):708714.
67. Li J, Lee L, Gong Y, Shen P, Wong S, Wise S et al. Bioassays for Estrogenic Activity:
Development and Validation of Estrogen Receptor (ERα/ERβ) and Breast Cancer
Proliferation Bioassays to Measure Serum Estrogenic Activity in Clinical Studies. ASSAY
and Drug Development Technologies. 2009;7(1):80-89.
68. Qin W, Zhu W, Shi H, Hewett J, Ruhlen R, MacDonald R et al. Soy Isoflavones Have an
Antiestrogenic Effect and Alter Mammary Promoter Hypermethylation in Healthy
Premenopausal Women. Nutrition and Cancer. 2009;61(2):238-244.
69. Ma H, Sullivan-Halley J, Smith A, Neuhouser M, Alfano C, Meeske K et al. Estrogenic
botanical supplements, health-related quality of life, fatigue, and hormone-related symptoms
in breast cancer survivors: a HEAL study report. BMC Complement Altern Med.
2011;11(1):109.
70. Bolca S, Urpi-Sarda M, Blondeel P, Roche N, Vanhaecke L, Possemiers S et al.
Disposition of soy isoflavones in normal human breast tissue. American Journal of Clinical
Nutrition. 2010;91(4):976-984.
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