Eating Soy Foods In Puberty May Protect Against Breast Cancer
Article Date: 10 Apr 2008 - 5:00 PDT
Evidence is growing from animal and human studies that genistein, a
potent chemical found in soy, protects against development of breast
cancer - but only if consumed during puberty, says a Georgetown
University Medical Center researcher in the British Journal of Cancer
published online. The challenge now, she says, is for scientists to
understand precisely why soy appears to provide a shield against the
most common cancer in women.
"Timing seems to be vitally important in use of this bioactive food,
and if we can figure out why that is so, then we may be able to help
prevent breast cancer in the widest sense possible," says the
researcher, Leena Hilakivi-Clarke, Ph.D., a professor of oncology at
the Lombardi Comprehensive Cancer Center at Georgetown.
Although there are a number of tantalizing theories to explain the
connection, "at the present time no convincing explanation can be
offered as to why the breast cancer-risk reducing effect of genistein
might be strongest during childhood and early adolescence,
Hilakivi-Clarke is a senior author of a review article published in
the journal that sums up the state of knowledge concerning the role
of early life genistein exposures in modifying breast cancer risk.
She has long studied the link between soy use and breast cancer, as
have her three co-authors, all Finnish researchers.
There have only been three human studies that tracked soy use during
puberty and later breast cancer development, and two of them focused
on Asian females, who eat soy in their traditional diet. But these
studies suggest soy offers a very strong protective effect - a 50
percent or more reduction in the risk of breast cancer - when soy is
eaten during childhood and adolescence.
The strongest evidence for genistein's protective effect comes from
studies in mice and rats, Hilakivi-Clarke says. For example, numerous
studies in rats show that the data regarding prepubertal exposure to
genistein are very consistent in showing a reduction in mammary
cancer risk, she says. Exposure to soy in fetal development or in
adult life does not have the same protective effect.
Further examination of experimental versus control rats demonstrated
that use of genistein in puberty cut the number of so-
called "terminal end buds" in the breast. These are the structures
that lead to growth of the mammary epithelium, which are the cells
lining milk ducts, etc., and it is in these epithelial cells that
breast cancer originates. But Hilakivi-Clarke says it is not clear if
a mere reduction in the number of these structures could reduce
cancer risk, or why.
Other studies suggest that genistein controls expression of genes in
terminal end buds that regulate cell growth, repair and death. For
example, the chemical could be controlling the ability of stem cells,
found on these buds, to reproduce themselves or to differentiate into
more specialized cells. "There is evidence that suggests that the
more stem cells there are on these structures, the greater the risk
of breast cancer development,
theory that breast cancer arises from stem cells that have lost
growth control.
Other associated research has found that the genes that genistein
appears to activate in developing mammary glands are well known ---
BRCA1, p53, and PTEN tumor suppressors, Hilakivi-Clarke says. These
genes repair genetic damage and control cell survival and death, and
they may also help control stem cell reproduction, she says, and
genistein apparently "up-regulates" these genes, boosting production
of their beneficial proteins.
What is perhaps most intriguing, she says, is that the same process
that protects the breast from excess growth during pregnancy seems to
be at work during puberty. "In pregnancy, BRCA1 is also up-regulated,
perhaps in order to control the fate of stem cells, allowing them to
make more cells for milk production, for example, but not more of
themselves."
So Hilakivi-Clarke favors the notion that genistein is acting as a
breast cancer protective just as an early first pregnancy in women is
known to protect against later development of the cancer:
"If malignancies occur in breast stem cells, then it is better that
many of these cells are differentiated earlier rather than later.
Pregnancy hormones do that, so the shorter time there is between
puberty and pregnancy, the greater that protection may be," she
says. "Genistein may also help control the fate of stem cells in the
same way."
"We think this is the mechanism by which genistein works, but we
really don't know and we need to find out," Hilakivi-Clarke
says. "The findings will matter."
------------
Article adapted by Medical News Today from original press release.
------------
Preparation of the review was supported by grants from the National
Cancer Institute (NCI), the National Institute of Environmental
Health Sciences (NIEHS), and the Academy of Finland. Co-authors
include Anni Warri, Ph.D., Niina Saarinen, Ph.D., and Sari Makela,
M.D., Ph.D., from the University of Turku in Finland.
About Lombardi Comprehensive Cancer Center
The Lombardi Comprehensive Cancer Center, part of Georgetown
University Medical Center and Georgetown University Hospital, seeks
to improve the diagnosis, treatment, and prevention of cancer through
innovative basic and clinical research, patient care, community
education and outreach, and the training of cancer specialists of the
future. Lombardi is one of only 39 comprehensive cancer centers in
the nation, as designated by the National Cancer Institute, and the
only one in the Washington, DC, area. For more information, go to
http://lombardi.
About Georgetown University Medical Center
Georgetown University Medical Center is an internationally recognized
academic medical center with a three-part mission of research,
teaching and patient care (through our partnership with MedStar
Health). Our mission is carried out with a strong emphasis on public
service and a dedication to the Catholic, Jesuit principle of cura
personalis -- or "care of the whole person." The Medical Center
includes the School of Medicine and the School of Nursing and Health
Studies, both nationally ranked, the world-renowned Lombardi
Comprehensive Cancer Center and the Biomedical Graduate Research
Organization (BGRO), home to 60 percent of the university's sponsored
research funding.
Source: Karen Mallet
Georgetown University Medical Center
http://www.medicaln
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