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Your Environment. Your Health.

Breast Cancer


woman breast cancer patient

You Can't Change Your Genes, but You Can Change Your Environment

Identifying and modifying environmental risk factors for breast cancer presents a tremendous opportunity to prevent breast cancer.

Approximately 246,000 women in the United States, or 1 in 8, are diagnosed with breast cancer each year. Breast cancer occurs when breast cells grow abnormally and invade either nearby or distant tissues. It is the second most common cancer among U.S. women, behind skin cancer.

Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, fluid coming from the nipple, or a red scaly patch of skin on the breast.

Breast cancer is more common in older women, and rarely occurs in men. In the US, white women are most likely to be diagnosed with breast cancer, but African-American women are most likely to die from the disease, according to the American Cancer Society.

What causes breast cancer?

NIEHS-funded research has clearly shown that breast cancer is caused by a combination of genetic, hormonal, and environmental risk factors.

But approximately 85% of breast cancers occur in women who have no family history of breast cancer, suggesting the importance of environmental factors. Since environmental factors may be identified and modified, NIEHS scientists and other experts in the field believe that prevention strategies are the best way to stop breast cancer before it starts.

Some environmental factors that have been consistently associated with increased breast cancer risk include:

  • Smoking
  • Alcohol
  • Exposure to ionizing radiation
  • Use of combination hormone therapy products
  • Being overweight or obese, especially after menopause
  • Taking diethylstilbestrol (DES), a synthetic estrogen given to pregnant women in the 1940’s to 1971 to prevent miscarriages or premature deliveries

Research also shows that more physical activity is linked to decreased breast cancer risk.

You can estimate your current risk for breast cancer using an online tool developed by NIEHS grantees.

What is NIEHS Doing?

Roughly 1 in 8 U.S.women will develop invasive breast cancer sometime during her life. (American Cancer Society, 2015)
Roughly 1 in 8 U.S.women will develop invasive breast cancer sometime during her life. (American Cancer Society, 2015)

Both in-house researchers and outside scientists funded by NIEHS are committed to searching for the origins of breast cancer, as well as strategies for prevention and treatment.

Sister Study – The study recruited more than 50,000 sisters of women with breast cancer from the United States and Puerto Rico. This landmark observational study has looked at lifestyle, early life factors, and environmental exposures, as well as genetic and biological factors that may increase breast cancer risk.

  • Burning wood or natural gas indoors at least once a week was associated with a modestly higher risk of breast cancer. (Abstract)
  • Women who developed diabetes during two or more pregnancies had a higher incidence of breast cancer. (Abstract)
  • Postmenopausal women who had higher vitamin D blood levels or who reported taking vitamin D supplements at least four times a week had lower rates of breast cancer. (Abstract)
  • Women who exercised or played sports more than seven hours a week when they were aged 5-19 had lower risk of breast cancer as adults. (Abstract)
  • While many measures of sleep quality were not associated with breast cancer risk, there was a positive association between having trouble sleeping four or more nights per week and increased breast cancer risk. (Abstract)

Two Sister Study – An offshoot of the Sister Study, this study focuses on breast cancer in women younger than 50, who can have different breast cancer risk factors than older women. Approximately 1,300 women with young-onset breast cancer are participating, along with their sisters (from the Sister Study) and their parents.

  • Women who have taken estrogen-only hormone therapy had a 42 percent decrease in their risk of young-onset breast cancer, compared to their sisters who had never taken hormone therapy. (Abstract)
  • Risk factors for young-onset breast cancer may differ from older-onset breast cancer, but few studies have focused on genetic variants that might be uniquely related to young-onset disease. In a family-based genome-wide association study of young onset breast cancer, three novel single nucleotide polymorphisms (gene variants) were found to be associated with young onset disease. (Abstract)

National Toxicology Program (NTP) – The NTP, an interagency program headquartered at NIEHS, is known for its expertise in conducting rodent studies that can be used to gain insights into the environmental origins of breast cancer and other diseases.

There are many similarities between human and rodent mammary glands and how they develop. Identifying environmental exposures that cause adverse mammary gland outcomes in rodents is a important first step in breast cancer prevention.

NTP researchers in the Reproductive Endocrinology Group are working to establish new methods to study mammary glands in rodent studies that can be consistently used and compared across labs. Several new findings (see abstracts below) may help researchers correctly identify abnormal growths and reduce false negative results. This will help scientists accurately identify environmental factors that lead to problems in mammary development or function. (Abstract, Abstract, Abstract)

More information about how environmental factors such as chemical exposures, dietary intake, alcohol consumption, and pharmaceuticals may contribute to breast cancer susceptibility is available in a special issue of the journal Reproductive Toxicology.

Breast Cancer and the Environment Program (BCERP) – In BCERP, grant-funded researchers and community organizations work together to discover environmental factors that may contribute to breast cancer. They also share lessons learned about breast cancer prevention with the broader community. BCERP is jointly funded by NIEHS and the National Cancer Institute.

In recent years, BCERP has studied how chemicals in the environment may affect the timing of puberty, because girls who get their periods early may have a higher risk of developing breast cancer as adults.

New BCERP projects are engaging racially and ethnically diverse communities because of poor breast cancer outcomes in African-American women. Additionally, BCERP is studying how environmental factors may affect intermediate risk factors for breast cancer, like increased breast density, that can precede disease.

Recent BCERP findings have shown:

  • Exposures to common contaminants in the environment may change the timing of puberty. For example, girls exposed to high levels of triclosan, a chemical used in antimicrobial soaps and hand sanitizers, experienced early breast development. Girls exposed to high levels of benzophenone-3, found in some sunscreens, experienced later breast development. (Abstract)
  • Changes in gene regulation that are age-dependent were found to occur during mammary tissue development in animals. This may help to explain why environmental exposures during breast development can increase breast cancer risk. (Abstract)
  • The proteins produced by developing mammary tissue may change after exposure to three common pollutants in the environment - bisphenol A, mono-n-butyl phthalate, and polychlorinated biphenyl 153. This may alter cell biology in ways that contribute to breast cancer. (Abstract)

The Interagency Breast Cancer and Environmental Research Coordinating Committee (IBCERCC)
IBCERCC is a congressionally mandated committee that was formed to examine the state of research on breast cancer and the environment in response to a 2008 law. NIEHS and the National Cancer Institute provided leadership for the committee, which included federal and non-federal representatives. In 2013, IBCERCC issued a comprehensive report to the secretary of the U.S. Department of Health and Human Services that recommended prioritizing prevention to reduce breast cancer, intensifying the study of chemical and physical risk factors, transforming research to include collaborations across scientific disciplines and with community organizations, and communicating the science to the public.

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)

Additional Resources

  • Disease Prevention Toolkit - Taking steps to protect your health is the best way to prevent disease and other conditions. Health screenings, vaccines, and guarding yourself from germs and bugs can help keep you feeling your best.
  • Healthy People 2020 - Healthy People provides science-based, 10-year national objectives for improving the health of all Americans.
  • Report on Carcinogens - The Report on Carcinogens (RoC) is a congressionally mandated, science-based, public health report that identifies agents, substances, mixtures, or exposures (collectively called "substances") in our environment that pose a hazard to people residing in the United States.

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