Approximately 230,000 women in the United States are diagnosed with breast cancer each year. Breast cancer is cancer (abnormal cell growth) that forms in tissues of the breast. 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. Invasive breast cancer is breast cancer that has spread to surrounding normal tissue from where it began in the breast lobules (milk glands) or ducts (thin tubes that carry milk from glands to nipple).
Breast cancer occurs in both men and women, although male breast cancer is rare. In the US, White women have the highest incidence rate for breast cancer, although African American/Black women are most likely to die from the disease.
What causes breast cancer?
NIEHS research has clearly shown that breast cancer is caused by a combination of genetic, hormonal, and environmental risk factors. Since environmental factors may be identified and modified, NIEHS scientists believe that prevention strategies are the best way to stop breast cancer before it starts.
Several environmental factors have been consistently associated with increased breast cancer risk:
- Use of combination hormone therapy products
- Use of oral contraceptives
- Exposure to ionizing radiation
- Being overweight or obese, especially after menopause
- 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 use this online tool, developed by NIEHS-funded grantees, to estimate your current risk for breast cancer.
What NIEHS is doing on breast cancer
You Can't Change Your Genes, but You Can Change Your Environment
Given that NIEHS research has clearly established that breast cancer is caused by a combination of genetic, hormonal, and environmental risk factors and we know that environmental factors can be identified and modified, focusing our efforts on prevention presents a tremendous opportunity to stop breast cancer before it starts.
Both in-house researchers, as well as outside scientists funded by NIEHS, are committed to searching for the origins, as well as potential prevention and treatment therapies for breast cancer.
Some key highlights from the Sister Study and our grantees are highlighted below.
The NIEHS-led Sister Study is the only long-term study in the United States and Puerto Rico of women ages 35 to 74 whose sisters had breast cancer. The study is following 50,000 women for at least 10 years to learn how environment and genes may affect the chances of getting breast cancer.
- Air pollution. Long-term exposure to fine particulate matter less than 2.5 micrometers in diameter and nitrogen dioxide, two components in ambient air pollution, were associated with higher blood pressure ( Abstract) and the risk of developing wheeze, a major symptom of asthma. ( Abstract). While there was no association between air pollution and breast cancer overall, findings in press show an increased risk of estrogen and progesterone receptor positive breast cancer (the most common subtype) associated with nitrogen dioxide air pollution.
- Ovarian hormone associated with breast cancer. Scientists found that blood concentrations of anti-Müllerian hormone, a biomarker for the size of the ovarian reserve, was positively associated with breast cancer risk. ( Abstract)
- Physical activity at work reduces breast cancer risk. Women who are more physically active at work are more likely to be active during leisure time. ( Abstract). Being physically active reduces the risk of breast cancer.
- Belly fat increases breast cancer risk. Women who have more weight around their waist and stomachs are more at risk for breast cancer. Waist circumference was found to be an important predictor of breast cancer risk for both premenopausal and postmenopausal women. ( Abstract)
- Tamoxifen for breast cancer prevention. Tamoxifen has been recommended for primary prevention of breast cancer. An evaluation of the risk benefit profiles of women taking tamoxifen in the Sister Study finds that while most women taking it are likely to benefit, many women discontinue use early presumably because of symptoms like hot flashes and some women who took the drug had insufficient evidence that the benefits outweighed the risks of serious side effects. ( Abstract)
- Chemical exposures in the workplace. Women with the highest levels of exposure to gasoline or petroleum products at work had an increased risk of breast cancer overall, and women exposed to soldering materials were at increased risk for developing breast cancer before menopause. ( Abstract)
- Young-onset breast cancer and hormone therapy. In the Two Sister Study, an offshoot of the Sister Study that focuses on young-onset breast cancer, estrogen hormone therapy was found to offer some protection against young-onset breast cancer, while combined estrogen and progestin hormone therapy was not associated with the disease. ( Abstract)
NIEHS-supported grantees are also working on breast cancer research. For example, NIEHS and the National Cancer Institute co-fund the Breast Cancer & the Environment Research Program (BCERP), which supports multidisciplinary scientists, clinicians, and community partners studying environmental exposures that occur throughout a woman's life and could predispose her to breast cancer.
- Exposures at every level may matter. NIEHS-supported researchers are now taking advantage of new science technologies to look at everything a person is exposed to through the course of a lifetime, referred to as the exposome, to determine risk cancers for breast cancer.
- DDT increases breast cancer risk. Women exposed prenatally to higher levels of the pesticide dichlorodiphenyltrichloroethane (DDT) were nearly four times more likely to develop breast cancer as adults than women exposed to lower levels before birth. ( Abstract)
- Phthalates and puberty. High-molecular weight phthalates were associated with later pubic hair development. This relationship was stronger among normal-weight girls compared to overweight girls. ( Abstract)
- High fat diet during puberty increases cancer risk. High fat diet during puberty can increase carcinogen-induced mammary cancer risk in adulthood without weight gain. Risk is not reversed by switching to a low fat diet in adulthood. ( Abstract)
- Meaningful messages needed for kids. Mothers with young daughters desire messages with greater scientific detail but presented in a more reader friendly format that includes greater explanation of findings. ( Abstract)
NIEHS Research Efforts
Stories from the Environmental Factor
- Environmental Factors and Breast Cancer Risk(1016KB)
- Breast Cancer and the Environment: Prioritizing Prevention(5MB)
- National Cancer Institute Breast Cancer Information
- National Cancer Institute Oral Contraceptives and Cancer Risk Information
- National Cancer Institute Video: Breast Cancer Statistics
- Report on Carcinogens
- Sister Study Newsletters
- Your genes, environment, and breast cancer risk: The Two Sister Study(273KB)