Looking for the Link
Between Environmental Toxins and Cancer
GINA KOLATA / NY Times 11aug02
DR. 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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