Tuesday, November 12, 2013
By Kerry Sheridan, AFP
WASHINGTON -- A decade-long research effort to uncover the
environmental causes of breast cancer by studying both lab animals and a group of
healthy U.S. girls has turned up some surprises, scientists say.
At the center of the investigation are 1,200 school girls who do not
have breast cancer, but who have already given scientists important new clues
about the possible origins of the disease.
Some risk factors are well understood, including early puberty, later age of childbearing, late onset of menopause,
estrogen replacement therapy, drinking alcohol and exposure to radiation.
Advances have also been made in identifying risky gene mutations, but
these cases make up a small minority. “Most of breast cancer, particularly in
younger women, does not come from family histories,” said Leslie Reinlib, a
program director at the National Institute of Environmental Health Sciences. “We
have still got 80 percent that has got to be environmental,” said Reinlib, who
is part of the Breast Cancer and the Environment Research Program (BCERP)
program that has received some US$70 million in funds from the U.S. government
since 2003.
Some of its researchers track what is happening in the human
population, while others study how carcinogens,
pollutants and diet affect the development of the mammary glands and breast
tumors in lab mice. The program's primary focus is on puberty because its early
onset “is probably one of the best predictors of breast cancer in women,”
Reinlib said.
Puberty is a time of rapid growth of the breast tissue. Research on
survivors of the Hiroshima atomic bombings in Japan has shown that those
exposed in puberty had a higher likelihood of developing breast cancer in
adulthood. The 1,200 U.S. girls enrolled in the study at sites in New York
City, northern California and the greater Cincinnati, Ohio, area beginning in
2004, when they were between the ages of six and eight.
The aim was to measure the girls' chemical exposures through blood and
urine tests, and to learn how environmental exposures affected the onset of
puberty and perhaps breast cancer risk later in life. Researchers quickly
discovered that their effort to reach girls before puberty had not been
entirely successful.
“By age eight, 40 percent were already in puberty,” said Reinlib. “That
was a surprising bit of information.” Further research has shown that the girls
appear to be entering puberty six to eight months earlier than their peers did
in the 1990s.
Obesity an Influencing Factor
A study published last week in the journal Pediatrics on this cohort of
girls found that obesity was acting as a primary driver of earlier breast
development. Other studies on the girls have focused on chemicals that are
known as endocrine disruptors
because they are believed to cause either earlier or later breast development.
Initial results showed “for the first time that phthalates, BPA, pesticides are in all the girls they looked at,”
said Reinlib. Researchers were taken aback by the pervasiveness of the
exposures, but also by the data which appeared to show some plastic chemicals
might not be as influential on breast development as some have feared.
“They didn't find much of an association between puberty and
phthalates, which are these chemicals that leach out of plastic bottles and
Tupperware,” Reinlib said. Another major finding regarded blood chemicals from
two nearby groups in Ohio and Kentucky, both drinking water that was apparently
contaminated by industrial waste.
Girls in northern Kentucky had blood levels of an industrial chemical —
perfluorooctanoic acid (PFOA or C-8) found in Teflon non-stick coating for pans
— three times as high as those who drank water from the Ohio River near
Cincinnati, where water was filtered with state-of-the-art technology.
“Northern Kentucky did not have granular activated carbon filtration”
in their water supply said researcher Susan Pinney, a professor at the
University of Cincinnati School of Medicine. “In 2012 they put it in after they
learned of our preliminary results.” Families were also notified of their
daughters' blood levels, she said.
The chemicals can linger in the body for years. Researchers were
dismayed to learn that the longer the girls spent breastfeeding as infants —
typically touted for its health benefits — the higher their PFOA levels
compared to girls who were fed formula.
What cannot be studied in the girls is tried on lab mice, who in one
experiment are being fed high-fat diets and exposed to a potent carcinogen to
see how the two interact. Mammary tumors develop much faster in the high-fat
diet group, said scientist Richard Schwartz of the Department of Microbiology
and Molecular Genetics at Michigan State University.
Fat mice have more blood supply in the mammary glands, higher
inflammation levels and display changes in the immune system. Follow-up studies
suggest that cancer risk stays high even if mice are fed high-fat diets in
puberty and switched to low-fat diets in adulthood, he told AFP.
“The damage is already done,” he said. “Does this mean that humans are
at risk the same way? We don't know that with certainty.” But the findings do
reinforce the advice that people often hear regarding how to maintain good
health — avoid fatty foods, maintain a normal weight and reduce chemical
exposures wherever possible, experts say.
Breast cancer is the most common cancer in women globally and took
508,000 lives in 2011, according to the World Health Organization.
https://www.chinapost.com.tw/health/cancer/2013/11/12/393410/Surprises-found.htm
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