The Search for Environmental Carcinogens

The news conference was held on Jan. 7, 1993, with breast cancer activists flanking Sen. Alfonse D’Amato (R-New York). The group was not satisfied with the findings of a study from the U.S. Centers for Disease Control and Prevention, which had just reported that elevated rates of breast cancer in Long Island could be explained by known risk factors. The women believed their illnesses had a deeper, more sinister explanation, perhaps a legacy of the agricultural roots of the now mostly affluent suburbs of New York City.

“We are taking matters into our own hands,” one of the women told reporters. And they did. With backing from D’Amato and other members of Congress, Public Law 103-43 was enacted later that year, directing the National Cancer Institute (NCI) and the National Institute of Environmental Health Sciences to study “environmental and other potential risks contributing to the incidence of breast cancer” in Nassau, Suffolk and Schoharie counties in New York and in Tolland County, Conn. The law instructed the investigation of environmental exposures, and even, to an unprecedented degree, how the studies were to be carried out.

"It was quite miraculous," says Karen Miller, founder of the Huntington Breast Cancer Action Coalition and a community advisor to the Long Island Breast Cancer Study Project. Few times in American history had ordinary citizens set the course of medical science. “There had never been a public outcry before,” she adds. But this was an era when advocates for breast cancer research were learning from AIDS activists about how to exert grassroots power over the scientific agenda.

“We each wanted to know, with a particular bent toward environment, why me?” Miller says. “What’s in the environment that contributed to my breast cancer?” In her view, and that of other Long Island women, government researchers were not looking hard enough or in the right places.

Almost 20 years later, the Long Island study and others have accumulated reams of data, yet experts remain troubled by the unanswered questions. The President’s Cancer Panel, appointed by President George W. Bush, concluded in 2010 “the true burden of environmentally induced cancer has been grossly underestimated.” It wasn’t just the statement, but the source, that got notice. Columnist Nicholas Kristof of The New York Times wrote, “It’s striking that this report emerges not from the fringe but from the mission control of mainstream scientific and medical thinking.”

We each wanted to know, with a particular bent toward environment, why me?

The science that connects any particular exposure to cancer takes a long and convoluted path, often with false starts and detours along the way. But there are other reasons why the identification of and protection against environmental exposures are not as straightforward as some people might hope. It’s not just that the science can be messy. Those who have a stake in the answer can influence the direction of research—as the Long Island women showed—to both the benefit and detriment of obtaining an answer. Sometimes patients themselves may fixate on the wrong threats. Sometimes industry, which benefits from as much scientific murkiness as possible, can keep doubt alive long after most scientists agree on an answer. (The tobacco industry proved to be quite successful at this technique.) And even after the research is done, different voices come to the table when government officials have to take the data and make decisions about which exposures need to be limited and by how much. “The landscape can get very complicated,” says Jonathan Samet, MD, director of the University of Southern California Institute for Global Health in Los Angeles.

The Toxic Substances Control Act, which was passed in 1976 and remains the law, does not require registration and health-effects testing of a chemical before it is put on the market (although it does require premanufacturing notification of new chemicals).

The Cancer Panel calculated that of the more than 80,000 chemicals in use today, only a few hundred have been tested for safety. We are literally born with them; nearly 300 chemicals have been found in umbilical cord blood. And even when something is known to cause cancer, that still doesn’t mean that it will be banned or that exposures will be heavily regulated. (Consider tobacco.)

That’s because, when deciding whether some exposure contributed to your cancer, the answer is: It depends.

“It depends on what it is and how you’re exposed,” Samet says. Something may be known to cause cancer but is still allowed on the market because the amount of exposure needed to cause cancer is more than someone would reasonably be exposed to. Or an exposure may cause cancer in animals, but not people. Remember the saccharine scares? Studies in animals in the 1970s suggested high levels of the artificial sweetener might contribute to bladder cancer. Only later did researchers determine that the cancer risk applied only to rats.

Some chemicals, such as the insecticide dichlorodiphenyltrichloroethane (DDT), are considered so toxic that their use is not allowed at all in the U.S. But most potential carcinogens are not so dangerous. Then the question becomes where to draw the line. Because they regulate different entities, the Environmental Protection Agency has different standards than the Food and Drug Administration, which has different standards than the Occupational Safety and Health Administration. And all during the process of setting the bar, politics can interfere. In June 2011, the government classified formaldehyde—which millions of Americans are exposed to daily—as a known human carcinogen, yet it remains a staple of plywood, hair salons, cosmetics and other products. Adding formaldehyde to the federal government’s 12th Report on Carcinogens was opposed by the chemical industry, despite studies that had long raised concerns.

[Why is it so difficult to pin down environmental causes of cancer?]

In December 2011, the Institute of Medicine, which advises the government on medical issues, released a much-anticipated report about breast cancer and the environment. Among other findings, the report’s authors acknowledged a lack of human evidence linking many environmental exposures to cancer. But, as the astronomer Carl Sagan was fond of saying, the absence of evidence is not evidence of absence.

[View the IOM's Breast Cancer and the Environment]

Regulatory agencies are supposed to base their decisions on science. The problem often is that the science can be open to interpretation. Take the Long Island Breast Cancer Study Project, which accumulated a vast database and led to more than 10 studies. The short answer, as summarized on the NCI website, says that the main study “did not identify specific environmental factors as a cause for breast cancer on Long Island,” but the actual picture is more complicated.

[What defines a cancer cluster?]

Two of the major chemicals examined on Long Island were polycyclic aromatic hydrocarbons (or PAHs) and organochlorine compounds (common to pesticides, such as DDT). PAHs are formed from the incomplete combustion of carbon-containing materials and are ubiquitous in the environment as part of air pollution, cigarette smoke or even the sizzle from your barbecue grill.

Research studies did not find a strong association with signs of organochlorine exposure in blood samples, but the results did suggest that PAH exposure may be associated with a higher risk of breast cancer. “We can’t rule that out,” says Marilie Gammon, PhD, of the University of North Carolina in Chapel Hill, who led the main study. The answer probably depends on a woman’s genetics; however, other factors may be at play, such as her age, weight gain or loss, diet or even the type of cancer she develops.

This highlights one of the biggest hurdles in investigating environmental exposures—not everyone who is exposed to a potential carcinogen will develop cancer. It depends on a person’s own genetics and other factors, even the time of life when a person is exposed. Researchers, such as Gammon and others, are still using the Long Island data to investigate the idea of “windows of susceptibility,” or those times in life, such as before birth, during childhood or puberty, when tissues may be particularly vulnerable to environmental threats. Furthermore, there is a long interval between the onset of exposure and actual development of cancer, a duration that can sometimes be as long as a few decades. During that length of time, a person is exposed to so many other potential hazards that cannot be controlled many other potential hazards that cannot be controlled but may influence the outcome.

The biggest question for consumers is how to protect themselves and their children when data are either absent, unclear or in the throes of political haggling. The government is supposed to provide guidance, but the President’s Cancer Council noted that “existing regulations, and the exposure assessments on which they are based, are outdated in most cases, and many known or suspected carcinogens are completely unregulated. Enforcement of most existing regulations is poor.” Jeanne Rizzo, RN, president and CEO of the Breast Cancer Fund, an organization that advocates for the elimination of preventable causes of the disease, summarizes it this way: “If we can’t even ban asbestos, then our regulatory system is failing us.”

Advocates have proposed stronger laws. In March 2011, David Christiani, MD, of the Harvard School of Public Health, called for regulations that would “require premarketing safety testing, reduce industry influence on regulations, and control the importation of toxic chemicals and products.” Writing in The New England Journal of Medicine, he said that we should move to a scientifically based, prevention-oriented approach: “That approach should be the cornerstone of a new national cancer-prevention strategy emphasizing primary prevention.”

Perhaps the biggest legacy of the Long Island project was not just the information it gathered, but how it encouraged scientists, community members and lawmakers to work together.

But protection doesn’t all fall to the government. Parents can choose foods, toys and household products that minimize children’s exposures to toxic chemicals. The President’s Cancer Panel also recommends using glass or stainless steel containers, which could also help reduce the demand for plastics and therefore the byproducts of their manufacture, and using filters on drinking water.

Lastly, experts advise not to get so concerned about chemicals that you lose sight of other known environmental cancer triggers. “The really big environmental causes of cancer are things like being overweight, smoking and inactivity,” says Walter Willett, MD, DrPH, of the Harvard School of Public Health. “I think it’s important that we do protect our environment as much as possible,” he says. Nonetheless, “it can be an unfortunate distraction from things we can do something about.”

Willett and others believe that the “toxic” environment would be better defined as those factors that lure children and adults into a lifetime of unhealthy eating patterns and do not encourage the establishment of safe places to ride a bike or play.

In the end, no one will ever be able to guarantee they won’t get cancer, nor will they ever truly know what caused their own disease. Perhaps the biggest legacy of the Long Island project was not just the information it gathered, but how it encouraged scientists, community members and lawmakers to work together in the search for answers, Miller says. “What we learned was that you needed to create a very strong and respected and comfortable relationship between these three players. That had not existed before.”

Editor’s Note: This article is the second in a two-part series. In the previous issue, we discussed environmental causes of cancer—how they are identified and proven—and how study results are ultimately presented to the larger scientific community for scrutiny and to the public for consideration."Connecting the Dots" appeared in the Winter 2011 issue.