Air Date: Week of October 15, 1993
Brenda Wilson reports on the movement among cancer researchers toward examining the link between breast cancer and chemicals found in the environment, including the pesticide DDT. The new momentum is due in part to two recent studies which suggested a link to between breast cancer and DDT and PCBs, both of which are chlorinated chemicals.
CURWOOD: This is Living on Earth, I'm Steve Curwood.
Probably few of us have been untouched by what has become an epidemic of breast cancer in the US. Malignant breast tumors strike one in every nine American women. Many are cured, but many are not, making breast cancer one of the leading causes of death. Part of what makes the disease so scary is the mystery surrounding its cause, and that its rate has risen steadily in recent years. Despite advances in detection and treatment, there has yet to be a scientific consensus on what causes the majority of breast cancer cases. There are some statistical links to early puberty, late child bearing, certain genes, and high alcohol and fat consumption. But these and other known risk factors account for only about 30 percent of U-S breast cancers cases. What causes the rest of these tumors? Some are pointing the finger at a group of toxic organic chemicals that contain chlorine. Originally developed in part as nerve gases, these compounds are found in many pesticides, such as DDT. They tend to concentrate in fat and fatty tissue. Researchers have been slow to explore the pesticide link to breast cancer. But as Brenda Wilson reports from Washington, that's beginning to change.
(Sound of party in progress)
WILSON: As Washington soirees go, this one is on the low-key and highly purposeful side. Evening wear festooned in pink ribbons and the presence of media stars offer indisputable evidence that breast cancer as a cause has arrived. This dinner, honoring First Lady Hillary Clinton, kicks off National Breast Cancer Awareness Month.
The dinner's sponsor, the pharmaceutical company Zeneca, is here to promote early screening, and the use of anti-cancer drugs and the mammography units that it manufactures. But detection is cold comfort for women who contend these cancers could have been prevented if women had not all too often been overlooked by the scientific community. Nancy Brinker is the founder of the Susan G. Komen Breast Cancer Foundation.
BRINKER: We are going to have to rededicate some of our research priorities to prevention. There have to be substances in our environment. It is so clear that some of these substances must be causing fatal and chronic diseases.
WILSON: Funding for breast cancer research has jumped from 43 to 300 million dollars since lobbying efforts began two years ago. Inquiries to the National Cancer Institute regarding the agency's research focus were directed to Dr. Aaron Blair, the chief of the Occupational Studies section, which investigates groups that may have been exposed to workplace or environmental carcinogens. Dr. Blair says political pressure is only one reason the Institute has begun to focus on the environment.
BLAIR: Two papers that came out last year, I think, would have launched some investigatory effort relating to environmental chemicals just by themselves, but because there are some groups that felt this was a good avenue to pursue, that had some impact on the way the government operates.
WILSON: The two papers were among the first to look at the possible link between pesticides and breast cancer. Specifically, scientists in separate studies at Mt. Sinai School of Medicine and the University of Michigan found significantly higher levels of DDT in the blood samples and fatty tissues of women who had been diagnosed with breast cancer than in women who were cancer free. There was also a weak link with PCBs. The New York study was careful to control for such risk factors as age, menopausal status, and socio-economics. The higher the levels of DDT, the greater the likelihood of breast cancer.
DDTs and PCBs are members of a huge class of chemicals known as organochlorines. They have been restricted in the US since 1972, but many others are still used in everything from pesticides and plastics to pharmaceuticals. Some have been known to cause cancer in animals, and they seem to have one important characteristic in common with the things that are known to cause breast cancer:
DAVIS: They all are related to the total amount of estrogen a woman is exposed to in her lifetime.
WILSON: Dr. Deborah Lee Davis is a senior policy on breast cancer at the Health and Human Services Department. Estrogens are hormones that are naturally found in the body and the environment that promote cell growth. But too much of them can lead to cancer-like cell growth. Davis and five other researchers in a recently issued paper argued that there are many compounds, not just organochlorines, found in the environment of industrial countries that mimic natural estrogens.
DAVIS: There are certain plasticizer compounds that are estrogenic, and they have been identified in both of these types of studies. There are also some volatile compounds such as the things you find out of automobile exhaust that have been found to be estrogenic.
WILSON: There are thousands of these chemicals. Most have never been tested to see if they mimic estrogen. Dr. Stephen Safe, a toxicologist at Texas A&M University, has no quarrel with what the Michigan and New York studies found, but he wonders about what they didn't find.
SAFE: Although it's true that there are lots of estrogens in the environment, in addition, there are a large number of anti-estrogens - compounds that, in theory, would protect against breast cancer. For example, in terms of organochlorine compounds, research in several labs, including my own, has shown that dioxin and related chemicals, including a number of PCBs are highly anti-estrogenic, and they would in fact counteract the activities of estrogens in the environment. Now what the balance is, I don't know. This is fact may help the situation in that at least some grant money's already been available for the studies and hopefully something good'll come of it.
WILSON: It seems that way, despite criticisms about the limitations of the two studies - their smallness, and lack of controls for all known risk factors. NCI's Dr. Aaron Blair cautions that they offer no proof of a connections between pesticides and breast cancer, but they provide promising leads.
BLAIR: So what we need is bigger studies that control better for all the other possible risk factors for breast cancer, so we can be pretty sure that if we see an association with, say, DDT and PCB, that it's not because these women consumed more alcohol or had a higher fat content in their diet. We have to make sure that it isn't due to things we already know that cause breast cancer.
WILSON: As a follow-up, Dr. Blair says NCI plans to investigate communities here and abroad where women are known to have worked with DDT or eaten foods contaminated by the pesticide, and it will survey communities to determine what risk factors may be contributing to clusters of high breast cancer rates.
Many women's groups and environmentalists don't want to wait for the final judgment. They want to see such pesticides banned altogether. Currently, the Environmental Protection Agency does not routinely screen pesticides to see if they are estrogenic, but the administration says that in a departure from previous administrations, it is already moving to reduce the use of these pesticides. Maybe, but for many women, the pace is not nearly fast enough. In Washington, for Living on Earth, I'm Brenda Wilson.
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