A decade-long research
effort to uncover the environmental causes of breast cancer by studying both
lab animals and a group of healthy US girls has turned up some surprises,
At the centre 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
Some risk factors are well
understood, including early puberty, later age of childbearing, late onset of
menopause, oestrogens replacement therapy, drinking alcohol and exposure to
Advances have also been
made in identifying risky gene mutations, but these cases make up a small
"Most of breast
cancer, particularly in younger women, does not come from family
histories," said Leslie Reinlib, a programme director at the National
Institute of Environmental Health Sciences.
"We have still got 80%
that has got to be environmental," said Reinlib, who is part of the Breast
Cancer and the Environment Research Programme (BCERP) programme that has received
some $70 million in funds from the US 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 tumours in lab mice.
Primary focus on puberty
The programme'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 US 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
discovered that their effort to reach girls before puberty had not been
"By age eight, 40%
were already in puberty," said Reinlib. "That was a surprising bit of
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 a primary driver
A study published last week
in the journal Paediatrics 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.
Chemicals linger for years
"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
"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
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 tumours 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.
High fat diets linked to cancer
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.
"It can't hurt, and it
can only help," said Schwartz.
Breast cancer is the most
common cancer in women globally and took 508 000 lives in 2011, according to
the World Health Organisation.