A detailed analysis of hundreds of completed breast cancer studies has linked disease development with environmental exposure to more than 200 chemical compounds.
The finding is part of an effort to build a free, online breast cancer database for researchers and the public.
Described as "the most comprehensive of its kind," the database will highlight growing concern about environmental carcinogens such as pollutants, food contaminants, and organic solvents. The scope of the project will also extend to work that explores risk-related lifestyle factors such as diet, levels of physical activity, smoking/drinking habits and body mass.
"This compilation is a great effort, because it summarises all the evidence and gives us hints of what to look for next," explained researcher Leslie Bernstein, a professor of preventive medicine with the Keck School of Medicine at the University of Southern California in Los Angeles.
The results are outlined in a supplement to the May 14th online issue of Cancer. The database is already accessible at either www.silentspring.org/sciencereview or www.komen.org/environment.
According to the American Cancer Society (ACS), carcinogens are defined as agents that instigate abnormal cell division or harmful changes in the structure of a cell's DNA. They include chemicals, radiation, or infectious agents, among other things.
Most chemicals not tested
The International Agency of Research on Cancer has already classified 90 or so compounds as human carcinogens, according to the ACS. But Bernstein's team said that most of the chemicals to which people are routinely exposed have not undergone any testing for carcinogenic risk. An estimated 80 000 chemicals are registered in the United States for commercial use, according to the researchers.
For more than two years, Bernstein worked alongside colleagues from Harvard University, the Roswell Park Cancer Institute, and the Silent Spring Institute to amass and sort through approximately 900 national and international breast cancer studies focused on carcinogens.
The team honed in on 460 human breast cancer studies, of which more than 150 looked at specific environmental carcinogens among breast cancer patients. Most of those studies were conducted in the 1990s.
The remaining studies involved animal or laboratory research. The researchers pointed out that animal studies are valid references, because all human carcinogens that have so far been tested in animals have also triggered tumours in animal subjects.
In the animal studies alone, evidence surfaced that linked 216 chemicals to the onset of breast tumours. These included 36 industrial chemicals, 6 chlorinated solvents, 18 products of combustion, 10 pesticides, 18 dyes, four type of radiation, 47 pharmaceuticals, and 17 hormones.
Specific compounds identified
Of these compounds, the researchers isolated 73 that can be found in either human food or consumer products.
They noted, for example, the lingering hazards associated with polychlorinated biphenyls (or PCBs), which were typically used in the production of electrical equipment until federally banned in 1979. PCBs continue to pose a risk via contaminated rivers, fish, and pre-existing building construction, the researchers warned.
In addition, the authors categorised 35 compounds as carcinogenic air pollutants, including polycyclic aromatic hydrocarbons (or PAHs), which are byproducts of combustion.
The team also drew attention to another group of 25 organic compounds, including dioxins, which are produced by waste incineration and manufacturing. These carcinogenic chemicals are present in many workplaces and place women at an increased risk for breast cancer, the researchers said. These include women working in machine shops, dry cleaners, hairdressers, glass manufacturers, and aircraft maintenance facilities, all of which use harmful organic solvents.
Furthermore, among the identified carcinogens, 29 are produced in large amounts - upwards of one million pounds or more per year.
The database project did not set strict guidelines as to how to limit exposure to carcinogens. But the authors said they encouraged research and government oversight into the problem. They advised that people do try and limit their exposure to PCB-contaminated fish, gasoline-generated air pollution, chlorinated tap water, non-stick coated cookware, and detergents containing fluorescent whiteners.
Extent of danger unknown
Just how carcinogenic, in terms of breast cancer risk, are these and other compounds on the list? The jury is still out on that question, Bernstein said.
"Women are terribly concerned about environmental causes of breast cancer," she said. "But it's really very difficult to study. Often the only way we've been able to look at some of these things is during occupational exposures or accidents - what we usually call disasters."
"So, this work is a very useful tool for those of us who want to try to understand what we've missed in breast cancer. Now, it's up to us to do something with all this information," Bernstein said.
Janet Gray, a professor of psychology and the director of the programme in science, technology and society at Vassar College in Poughkeepsie, New York, called the new database "an enormous contribution."
"Its greatest value is just the sheer comprehensive nature of the work, which allows both the public and researchers to have access to huge amounts of information in one place," she said. "I think this effort will really move us forward." – (HealthDayNews)
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