PROOF
Looking for the Link
By GINA
KOLATA
 R.
DEBORAH WINN has had breast cancer herself, so when she speaks to
women who have just received the dread diagnosis, she understands
the nagging question: Why did this happen to me? Many people suspect
environmental pollutants like pesticides, for instance, or car
exhaust. But Dr. Winn, head of the extramural epidemiology program
at the National Cancer Institute, which conducts studies to look for
environmental causes of cancer, does not tell women that pollutants
are the cause.
"Usually, I tell them that there are a lot of factors that
combine — it's a multistep process," Dr. Winn said. "There is no one
thing. Many aspects of your reproduction are involved. It may have
something to do with your genes and in how you repair damage, how
you metabolize estrogen."
Dr. Winn, like many other scientists, said that the quest for
environmental causes of cancer — from chemicals in the water to
electromagnetic fields near power lines to radiation from a
cellphone — may be more daunting than the public realizes.
Conclusive evidence that any of these things increase one's risk of
cancer has never been found, despite repeated studies. And even if
there is a link, several experts said, it may be beyond the capacity
of science to find it.
Still, the drive to blame something other than chance is a strong
one, and the issue arose again last week when a long-awaited study
of breast cancer on Long Island did not find evidence that certain
pesticides, exhaust fumes, or cigarette smoke were linked to cancer.
The $8 million study, which was financed by Dr. Winn's group at the
National Cancer Institute, came into being because local advocates
had pressured Congress to approve it. When earlier studies found
that breast cancer rates in Nassau and Suffolk counties on Long
Island were about 3 percent higher than the national average,
advocates were certain that this new study would find a smoking gun
in the environment.
Instead, scientists said, the investigation raised questions
about what sort of assurances research like this can really provide.
Geri Barish, the president of 1 in 9: The Long Island Breast
Cancer Action Coalition, said that she knows that the pollutants
studied are dangerous — they cause cancer in laboratory animals, she
said. "How could they absolutely say that a known carcinogen is not
absolutely involved in the cause of cancer?" she asked.
DR. WINN points to the study, which examined blood and urine from
more than 3,000 Long Island women for evidence of exposure to DDT,
PCB's, chlordanes or chemicals from cigarette smoke. The scientists
also looked at carpet dust, tap water and yard soil for evidence
that the chemicals were in the women's environment. But those who
got breast cancer were no more likely to have been exposed to the
chemicals than those who didn't.
The data, she said, "were very, very conclusive."
The chemicals that were examined were thought to be plausible
culprits — largely because they could cause cancer in mice. Still,
Dr. Winn said, "In the study, it is clear that they are not
associated with breast cancer."
The one tentative link was a very modest increase in risk from
exposure to polycyclic aromatic hydrocarbons, chemicals that are in
grilled food and in cigarette smoke. But Marilie D. Gammon, the Long
Island study's lead investigator and an epidemiologist at the
University of North Carolina, discounts the connection, saying the
effect was minuscule and the risk did not go up with greater
exposure, as it should have if the chemicals were causing breast
cancer. Smokers, for example, did not have more breast cancer than
nonsmokers.
The results in Long Island were consistent with previous studies.
For example, a study published in the New England Journal of
Medicine in 1997, involving 32,826 nurses, also found no evidence
that DDT and PCB's increase the risk of breast cancer.
The next year, Dr. David Hunter, director of the Harvard Center
for Cancer Prevention, and his colleagues published a paper in The
Journal of the National Cancer Institute that pulled together data
from five studies involving 1,600 women. Again no link between
exposure to the chemicals and breast cancer was found.
"I think we have the answers for these chemicals," Dr. Hunter
said.
BUT what if the risks are very small and the exposures took place
in the distant past? Then, Dr. Gammon said, it can stretch the
limits of science to try to find an association.
"In some areas of science we can do wonderful things," Dr. Gammon
said. "But there are still some very basic things we can't do. We
don't have accurate ways to measuring pollutants from a long time
ago."
Dr. John Boice, the scientific director of the International
Epidemiology Institute in Rockville, Md., mentions other
complications. "Often the exposure you are looking for, whether it
is indoor radon or pesticides or solvents in the water, are so low
that it is difficult to find an effect even if one is there." In
addition, he said, it is hard even to find people who may have been
exposed to low levels of a pollutant 10 or 20 years ago. "People
move, they migrate," he said.
Dr. Michael Gallo, the associate director for cancer prevention
at the Robert Wood Johnson Medical School's cancer institute, said
the same. "Looking for direct causation is going to be impossible,"
he said.
Indeed, beyond cigarette smoking, excessive sun exposure, radon,
very high concentrations of arsenic in water and, possibly, air
pollution, very few environmental causes of cancer have been proven
definitively. But advocates who pushed for the Long Island study are
not easily dissuaded. Dr. Gammon said she had been meeting with the
women, trying to explain the limits of science. "They don't want to
hear it," she said.
Ms. Barish said she was not at all convinced that the pollutants
were not causing breast cancer.
"I refuse to accept the fact that they didn't find anything," she
said. "They didn't find anything conclusive because in the
scientific world it has to be exact." But, she added, "they couldn't
say 100 percent that there wasn't a link." And so, Ms. Barish said,
the story is not over. "We need to do a lot more studies," she said.
Others said it may be time to close the books. "I think it is
important that these studies have been done," said Dr. Barbara Hulka,
an emeritus professor of epidemiology at the University of North
Carolina. "We ought to be on the cautious side." But this and other
studies of environmental pollutants and cancer have not found the
suspected link, she said. "There comes a point after so many studies
are done that it becomes less productive to continue that line of
work."
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