More women in the United States are diagnosed with breast cancer than any other type of cancer. This year alone, the National Cancer Institute estimates that there will be close to 180,000 new cases and over 40,000 deaths from the disease. And while simply growing older and having a family history of breast cancer are considered major risk factors, these factors only account for about a quarter of breast cancer cases, according to the American Cancer Society. In other words, for about seventy-five percent of all breast cancer cases, there are other forces at work. Some scientists and many in the general public feel that those risk factors could include endocrine disrupters: environmental contaminants that act like hormones.

The hypothesis that certain chemicals have the ability to mimic or block hormones like estrogen and disrupt the body's own hormonal balance has particular resonance for some seeking to explain the high rates of breast cancer. This is because breast cancer, like prostate cancer, is a hormone dependent cancer. Women who start their periods early in life, end them later, have fewer children or have their children later increase their lifetime exposure to the female hormone estrogen. Researchers believe this increased estrogen exposure may put some women at greater risk for developing breast cancer.

Whether or not man-made chemicals that the body thinks are estrogen actually play a role in the incidence of breast cancer remains an unanswered scientific question. But what cannot be disputed is the role that this notion has played in bringing government attention and dollars to the issue of endocrine disruption. Possible links to breast cancer is one reason the Clinton administration has made researching the hypothesis a top environmental priority.

In the early 1990s, it became apparent that women on Long Island faced a higher risk of breast cancer than women in other parts of New York. According to the New York State Department of Health, from 1980 through 1988 there were 116.14 cases of breast cancer for every 100,000 women in Nassau County. The numbers from Suffolk County were slightly lower at 112.54. These numbers contrasted with 96.3 cases of breast cancer per every 100,000 women statewide. Studies looking into why the rates were higher in Nassau and Suffolk counties found that many women there had some known risk factors for the disease. These included being affluent, Jewish, postponing childbirth until later in life, and the absence breastfeeding. Women on Long Island were outraged that no one was looking into environmental causes of their disease.

Out of their anger, they formed the group "One-in-Nine: The Long Island Breast Cancer Action Coalition" in 1990. The group took its name from what the American Cancer Society says are a woman's chances of contracting the disease if she lives to be 85 years old. Just a few weeks later the National Breast Cancer Coalition was formed and women with breast cancer became a political force. Members of One-In-Nine met with and persuaded Senator Alfonse D'Amato (R-NY) to help them secure more funding for disease research. Their efforts paid off. In 1993, D'Amato, with the help of Senator Tom Harkin (D-IA), was able to multiply a $25 million line in the Department of Defense budget to $210 million for breast cancer research.

That same year, Congress directed the National Cancer Institute to begin a study looking at environmental factors and breast cancer in Long Island and two other counties in the Northeast. Known as the Long Island Breast Cancer Study Project, it is actually a collection of over ten different studies being conducted at research institutions throughout the Northeast. The project's major study is being headed by Marilie Gammon at Columbia University. Gammon and her colleagues are trying to determine if the pesticide DDT contributes to breast cancer. Results from this as well as the other studies are expected in the next few years. All told, the National Cancer Institute estimates that it is spending at least $20 million on the research.

Also in 1993, Mary Wolff, an associate professor at Mount Sinai Medical Center in New York, authored a paper indicating that exposure to certain chemicals may indeed play a role in the disease. Wolff's study, published in the Journal of the National Cancer Institute, found that women who had high blood levels of DDE, a DDT breakdown product, had a much greater risk of developing breast cancer -- four times higher than women with low levels of DDE. DDT, an insecticide banned in the US in the 1970s, can mimic the hormone estrogen and is a known endocrine disrupter. It was used heavily on Long Island earlier in this century.

Wolff looked at blood samples from 58 women in New York who developed breast cancer and compared them with 171 women who didn't have cancer. In addition to DDT, Wolff looked at another hormone disrupting contaminant: a class of banned chemicals known as PCBs, which were used to insulate electrical transformers. While the PCB levels were slightly higher in women with breast cancer, the elevated levels were determined to be statistically insignificant.

Wolff's 1993 study was small but it got a huge response from activists, the media, and politicians. For the women in Long Island, it was new evidence that the environment may have played a role in their cancers.

Before it became a suburban mecca, Long Island was farmland. In the 1940's it was the nation's largest potato growing region and home to a USDA sponsored program to quarantine a pesky potato-eating worm called the Golden Nematode. Millions of gallons of pesticides, including DDT, were poured into area fields.

After Wolff's study came out, Long Island's newspaper Newsday ran a series of stories on breast cancer and the island. The paper looked into the history of chemical use in the area -- pesticides like aldicarb, chlordane, types of dichloroprane and others. The paper reported that many of these chemicals had not been tested for their abilities to mimic hormones, and that the government did not require this sort of screening.

Within days of the Newsday stories about Long Island, politicians in Washington were calling for change. In the House of Representatives, Henry Waxman (D-CA), then the head of the subcommittee on Health and the Environment announced he would work to pass legislation requiring that all pesticides be screened for their ability to mimic estrogen. Senator D'Amato vowed to do the same. In 1996 President Clinton signed the Food Quality Protection Act which included their requirement that the EPA develop a way to screen chemicals for estrogenicity by the end of 1998.

Since Mary Wolff's 1993 study, more papers have come out on the subject. Ironically, a study co-authored by Wolff herself downplayed DDT's and PCBs' connections to breast cancer. The study, published in the New England Journal of Medicine in October of 1997 analyzed frozen blood samples taken from nurses in 1989 and 1990. Blood samples from 240 nurses who subsequently developed cancer were compared with control samples from nurses without cancer. The results showed that the women with cancer did not have higher levels of DDT breakdown products or PCBs in their blood.

To confuse matters more, other scientists have come forward to say that certain PCBs, breakdown products of DDT, and other known toxins like dioxin might actually prevent breast cancer. These chemicals can act as anti-estrogens which have the ability to protect against the disease. Dr. Steve Safe of Texas A&M asserted this in an editorial published in the same issue of the New England Journal of Medicine as Wolff's more recent study.

But some researchers say there are questions about whether the current studies have focused on the correct timing of a woman's exposure to environmental estrogens. Many activists and researchers, including Wolff herself, have noted that it may not be the amount of chemicals present in a woman's body at the time she gets cancer that is important, but rather her levels of exposure when her breasts are just developing at puberty. Others suggest it may even be fetal exposure in the womb that is important. In addition, there are countless chemicals in addition to DDT and PCBs that have not yet been tested for their links to breast cancer.

Experts agree that the issue is far from resolved, nor should it be. A spokeswoman from the American Cancer Society said that even though there isn't yet any significant evidence to indicate that estrogenic chemicals are causing breast cancer, the matter needs to be studied further. Because breast cancer is clearly a disease based on estrogen exposure, she stressed that all types of potential exposure -- natural and man-made -- should be studied.

In the next few years, results from the Long Island Breast Cancer Study Project will be adding new data to this debate. And other studies will likely weigh in. As women wait for more information about estrogenic chemicals and breast cancer there are proactive things they can do to try and prevent the disease, like getting screened regularly, eating lots of fruits and vegetables, keeping their weight down and cutting back on alcohol and tobacco intake.