Breast Cancer

Introduction

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

Breast Cancer and the Environment: Prioritizing Prevention (5MB)

Identifying which environmental factors may increase the chance of developing breast cancer is the first step in figuring out how to avoid them.

About 12%, or 1 in 8, women in the U.S. will develop breast cancer during their lifetime. It is the second most common cancer among U.S. women, behind skin cancer. ¹ Breast cancer occurs mostly in women who are 50 years old or older. But men can also develop the disease. Each year in the U.S., about 245,000 cases of breast cancer are diagnosed in women and about 2,200 in men. ²

Breast cancer is a disease in which cells in the breast grow out of control and may form a tumor. There are different kinds of breast cancer. If the cancerous cells spread to other parts of the body, the disease is called metastatic breast cancer.

Although scientists have identified many risk factors that increase a woman’s chance of developing breast cancer, they do not yet know what causes normal cells to become cancerous. Experts tend to agree that breast cancer is caused by a combination of genetic, hormonal, and environmental factors.

Breast Cancer and the Environment

Most women who develop breast cancer have no family history of the disease, suggesting an environmental link.

Both the President’s Cancer Panel and the Interagency Breast Cancer and Environment Research Coordinating Committee have reported on the mounting literature demonstrating connections between exposures to environmental toxicants and later development of disease, including breast cancer. They have also prioritized prevention as an aim for both research and public health practice. A 2017 state of the evidence publication reinforces the conclusion that exposures to a wide variety of toxicants, many found in everyday products, can lead to an increased chance of developing breast cancer.

NIEHS scientists and other experts believe prevention strategies are the best way to try to stop breast cancer before it starts.

Fact Sheets

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Breast Cancer Risk and Environmental Factors

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Cáncer De Mama: Por Qué Importa El Medio Ambiente

What Is NIEHS Doing?

NIEHS plays a leadership role in funding and conducting studies on the ways in which environmental exposures increase breast cancer risk. This research seeks to understand the role of environmental agents, such as toxic chemicals, in the initiation and progression of cancer, as well as genetic susceptibility. Identifying and reducing contact with environmental factors linked to breast cancer presents tremendous opportunity to prevent this disease.

Sister Study– The NIEHS Sister Study has recruited more than 50,000 sisters of women with breast cancer from the U.S. and Puerto Rico. This landmark observational study is looking at lifestyle and environmental exposures, as well as genetic and biological factors that may increase breast cancer risk. Important findings from this study follow.

• Biologic age, a DNA-based estimate of a person’s age, is associated with future development of breast cancer. For every five years a woman’s biologic age was older than her chronologic or actual age, known as age acceleration, she had a 15% increase in her chance of developing breast cancer. ³
• Women who lived in areas with higher levels of lead, mercury, and cadmium in air pollution had a greater chance of developing postmenopausal breast cancer. ⁴
• Postmenopausal women who had higher levels of vitamin D in their blood or who reported taking vitamin D supplements at least four times a week had lower rates of breast cancer. ⁵
• Vitamin D may protect against breast cancer, including Black/African American and non-Black Hispanic/Latina women. NIEHS researchers found women with low vitamin D levels have a higher risk of breast cancer than those with sufficient vitamin D levels.
• Burning wood or natural gas indoors, at least once a week, was associated with a modestly higher risk of breast cancer. ⁶
• Women who developed diabetes during two or more pregnancies had a higher incidence of breast cancer. ⁷
• Women who exercised or played sports more than seven hours a week during ages 5-19 had lower risk of breast cancer as adults. ⁸
• An association was found between having trouble sleeping four or more nights per week and increased breast cancer risk. ⁹

Two Sister Study – An offshoot of the Sister Study, this study focuses on breast cancer in women younger than 50, who may 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 biological parents. Some results from the study include the following.

• A 2020 study observed that women who drank at least five cups of green or black tea per week, as compared to not drinking any tea, were less likely to develop breast cancer. The reported association did not vary according to menopausal status or body weight and height. The results should not be interpreted as meaning tea drinking can prevent breast cancer.
• Red meat consumption may increase the risk of invasive breast cancer, whereas poultry consumption may be associated with reduced risk. Substituting poultry for red meat could reduce breast cancer risk.
• In women with a family history of breast cancer, physical activity (7 or more hours per week) was associated with reduced breast cancer risk in postmenopausal women. This result is consistent with other studies finding a link between more physical activity and reduced chance of breast cancer.
• Diets that create a higher acid load (associated with meat protein and grains) in the body may be a risk factor for breast cancer, while diets that create an alkaline load (associated with vegetables and fruits) may be protective against hormone receptor negative breast cancer.
• Women who took estrogen-only hormone therapy had a 42% decrease in their risk of young-onset breast cancer, compared to their sisters who never had hormone therapy. ¹⁰
• Three novel single nucleotide polymorphisms, or genetic variation, were associated with the disease in younger women. ¹¹

In-house NIEHS researchers have also studied how environmental exposures can interact with genetic factors to affect breast cancer risk.

• Women living in areas with higher levels of air pollution, particularly PM 2.5 and other traffic-related pollutants, may have a greater chance of developing breast cancer. This result is based on a large study of about 1,900 demographically diverse women. The subgroup in the study who had the highest air pollution exposure were non-Hispanic Black women living in Midwestern urban areas.

Breast Cancer and the Environment Program (BCERP) – Jointly funded by NIEHS and the National Cancer Institute, grant-funded researchers and community organizations worked together through BCERP to discover environmental factors that may contribute to breast cancer. This program, which began in 2003 and wound down by 2020, was one of the first at NIEHS to require transdisciplinary expertise. It used a team science approach, including toxicology, epidemiology, environmental health, biostatistics, and communication, to address research questions and facilitate community engagement.

An overarching concept from BCERP is that the influence of environmental chemicals on breast cancer risk may be greater during certain windows of susceptibility in a woman’s life, including prenatal development, puberty, pregnancy, and the menopausal transition. By focusing on environmental chemical exposure during specific periods when breast tissue changes, we may identify when prevention efforts are more likely to be effective.

Some hallmark findings from BCERP follow.

Roughly 1 in 8 U.S. women will develop invasive breast cancer sometime during her life. (American Cancer Society, 2019)

• The chance of developing breast cancer is increased with exposure to endocrine disrupting chemicals during these periods in a woman's life: her prenatal development, puberty, pregnancy, and menopausal transition. ¹²
• 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, experienced early breast development. Also, girls exposed to high levels of benzophenone-3, found in some sunscreens, experienced later breast development. ¹³
• Proteins produced by developing mammary tissue may change after exposure to bisphenol A, a chemical found in many plastic products, and other pollutants in the environment. These exposures may alter cells in ways that contribute to breast cancer.
• DDT exposure during pregnancy may alter certain genes leading to an increased chance of developing breast cancer in the daughters of those women.

National Toxicology Program (NTP) – Headquartered at NIEHS, NTP is an interagency program known for expertise in conducting studies into the environmental origins of disease, including breast cancer. For example, researchers in the Reproductive Endocrinology Group are establishing new methods to study mammary glands. Sharing these methods with other labs will help scientists accurately identify environmental factors that may lead to problems in mammary gland development or function.

The Interagency Breast Cancer and Environmental Research Coordinating Committee (IBCERCC) – Supported by NIEHS and the National Cancer Institute, IBCERCC was authorized by the Breast Cancer and Environmental Research Act of 2008 (Public Law 110-354) to examine the state of research on breast cancer and the environment. The committee included federal and non-federal representatives. IBCERCC issued a comprehensive report in 2013 that stated prevention is the key to reducing the emotional, physical, and financial burden of breast cancer. It also recommended 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)

• Increasing Evidence Links Air Pollution With Breast Cancer (November 2021)
• New Breast Cancer Risk Score Developed by NIEHS Scientists (October 2021)
• Breast Cancer and Air Pollution Linked by New Marker (November 2020)
• Breast Cancer Awareness Seminar Draws Hundreds (November 2020)
• Communication Tools Support Breast Cancer Prevention Efforts (March 2020)
• Blood Test May Point to Timing of Breast Cancer Diagnosis (February 2020)
• Permanent Hair Dye and Straighteners May Increase Breast Cancer Risk (January 2020)

Press Releases

• Permanent Hair Dye and Straighteners May Increase Breast Cancer Risk (Dec. 4, 2019)

Additional Resources

• Mammograms - Information by the Office of Women’s Health, U.S. Department of Health and Human Services.
• National Cancer Institute - Facts, risk factors, diagnosis, and treatment of breast cancer.
• Centers for Disease Control and Prevention - Basic information about low-cost screening, treatment plans, statistics, and other resources related to breast cancer.
• National Library of Medicine - Research, genetics, causes and prevention, and other helpful information.

Related Health Topics

• Air Pollution and Your Health
• Epigenetics
• Gene-Environment Interactions