An estimated 12.4% of women born in the US today will develop breast cancer at some point during their lives. Past research has indicated that exposure to some chemicals may increase the risk of breast cancer. Now, a new study has identified 17 "high-priority" chemicals women should avoid in order to reduce such risk and demonstrates how their presence can be detected.
Scientists from the Silent Spring Institute in Massachusetts say their findings, recently published in Environmental Health Perspectives - a journal from the National Institutes of Health (NIH) - significantly advance breast cancer prevention efforts.
"The study provides a road map for breast cancer prevention by identifying high-priority chemicals that women are most commonly exposed to and demonstrates how to measure exposure," explains study author Ruthann Rudel, research director of the Silent Spring Institute.
"This information will guide efforts to reduce exposure to chemicals linked to breast cancer, and help researchers study how women are being affected."
According to the research team, only 5-10% of breast cancers are a result of high-risk inherited genes. Furthermore, they note that around 80% of women diagnosed with breast cancer are the first in their family to develop the disease. Such figures, the researchers say, are evidence that breast cancer is caused by additional factors.
Identifying breast cancer carcinogens
It is well documented that exposure to some chemicals, including alcohol, tobacco smoke and those involved in combination hormone replacement therapy, may increase the risk of breast cancer in women.
But the researchers note that many other chemicals have been shown to cause mammary tumors in animals. However, only a small number of these chemicals have ever been incorporated in human breast cancer studies, partly because there have been no reliable techniques through which to measure exposure.
Therefore, the team set out to determine what chemicals present the highest risk of breast cancer in women and how exposure to such chemicals can be measured.
Firstly, the researchers identified 216 chemicals that have been associated with mammary tumors in rodents, before identifying 102 that women were most likely to be exposed to.
The team then reviewed exposure to such chemicals in rodent studies and compared the results with human breast cancer studies. This was to see whether rodent studies could be used to predict human study results.
The researchers assessed studies in which researchers had measured breakdown products (metabolites) of each chemical or the chemical itself in the blood, urine or other samples of humans. This was to determine the best way for researchers to measure exposure to carcinogens.
Gasoline and chemicals formed by combustion are biggest 'mammary carcinogens'
The researchers consolidated the identified chemicals into 17 high-priority groups that may cause breast cancer in women.
The greatest sources of breast cancer carcinogens in the environment were found to be gasoline and chemicals created by combustion, such as benzene and butadiene. Such chemicals are present in vehicle fuel, lawn equipment, tobacco smoke and burned or charred food.
Solvents including methylene chloride and other halogenated organic solvents - often found in industrial degreasers, speciality cleaners and spot removers - were found to be other breast cancer-causing chemicals.
Other mammary carcinogens include chemicals found in flame retardants, stain-resistant textiles, hormone replacement therapy and drinking water disinfection byproducts.
The team found biomarkers in urine, blood and other samples for 62 of the 102 high-priority breast cancer carcinogens identified that could be used to measure women's exposure. They discovered that techniques used in rodents could be used to identify a further 11 chemicals in humans.
Study author Julia Brody, PhD, executive director at Silent Spring Institute, says that the association between toxic chemicals and breast cancer has "largely been ignored" so far, adding:
"Reducing chemical exposures could save many, many women's lives. When you talk to people about breast cancer prevention, chemical exposure often isn't even on their radar. Studies that address toxic chemical exposure account for just a drop in the bucket of money spent on breast cancer."
However, this latest research could change this. The NIH plan to use the findings in their upcoming study of sisters involving more than 50,000 women, which will look into the causes of great cancer.
"This paper is a thorough review of toxicology data and biomarkers relevant to breast cancer in humans," says Dale Sandler, PhD, chief of epidemiology at NIH's National Institute of Environmental Health Sciences (NIEHS) and researcher involved in the forthcoming study.
"It's a terrific resource for epidemiologists thinking about studying environmental contributors to breast cancer or trying to understand the associations they see in their questionnaire data. This is a valuable compendium that should help me in my work with the Sister Study cohort."
Steps to reduce exposure to mammary carcinogens
But for now, the researchers say there are a number of things women can do to reduce their risk of exposure to mammary carcinogens, including:
- Limiting exposure to fumes from gasoline
- Limiting exposure to exhaust from diesel and other fuel combustion, such as from vehicles or generators
- Use electric instead of gas-powered lawn mowers
- Use a ventilation fan when cooking and reduce consumption of charred or burned food
- Avoid stain-resistant rugs, fabrics and furniture
- Use a solid carbon block drinking water filter
- Remove shoes at the door, use a vacuum with a HEPA filter and clean with wet rags and mops to reduce exposure to chemicals in house dust.
Medical News Today recently reported on a study from the National Cancer Institute, which suggested that contrary to previous research, fertility drugs may not increase the risk of breast cancer.