- What is breast cancer
- What are the risk factors for breast cancer?
- Breast cancer risk factors you cannot change
- Lifestyle-related risk factors for breast cancer
- Factors with unclear effects on breast cancer risk
- Disproven or controversial breast cancer risk factors
- Can breast cancer be prevented?
- Signs and symptoms of breast cancer
- American Cancer Society recommendations for early breast cancer detection in women without breast symptoms
- Paying for breast cancer screening
- References: Breast cancer prevention and early detection
Breast cancer risk factors you cannot change
Simply being a woman is the main risk factor for developing breast cancer. Men can develop breast cancer, but it’s about 100 times more common among women than men. This is probably because men have less breast tissue, as well as less of the female hormones estrogen and progesterone, which can promote breast cancer cell growth.
Your risk of developing breast cancer goes up as you get older. About 1 out of 8 invasive breast cancers are found in women younger than 45, while about 2 of 3 invasive breast cancers are found in women age 55 or older.
Inheriting certain genes
About 5% to 10% of breast cancer cases are thought to be hereditary, meaning that they are caused by gene defects (called mutations) passed on from a parent.
BRCA1 and BRCA2 gene changes: The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 or BRCA2 gene. In normal cells, these genes help prevent cancer by making proteins that help keep the cells from growing out of control. If you inherited a mutated copy of either gene from a parent, you have a high risk of developing breast cancer during your lifetime.
Although in some families with BRCA1 mutations the lifetime risk of breast cancer is as high as 80%, on average this risk seems to be in the range of 55 to 65%. For BRCA2 mutations the risk is lower, around 45%.
Breast cancers linked to these mutations occur more often in younger women and more often affect both breasts than cancers not linked to these mutations. Women with these inherited mutations also have an increased risk for developing other cancers, particularly ovarian cancer.
In the United States, BRCA mutations are more common in Jewish people of Ashkenazi (Eastern Europe) origin than in other racial and ethnic groups, but they can occur in anyone.
Changes in other genes: Other inherited gene mutations can also lead to breast cancer. These gene mutations are much less common and often do not increase the risk of breast cancer as much as the BRCA genes.
- ATM: The ATM gene makes a protein that normally helps repair damaged DNA. Inheriting 2 abnormal copies of this gene (one from each parent) causes the disease ataxia-telangiectasia. Inheriting one abnormal copy of this gene has been linked to a high rate of breast cancer in some families.
- TP53: The TP53 gene makes a protein called p53 that helps stop the growth of abnormal cells. Inherited mutations of this gene cause Li-Fraumeni syndrome. People with this syndrome have an increased risk of breast cancer, as well as other cancers such as leukemia, brain tumors, and sarcomas (cancers of bones or connective tissue). This is a rare cause of breast cancer.
- CHEK2: The Li-Fraumeni syndrome can also be caused by inherited mutations in the CHEK2 gene. Even when it doesn’t cause this syndrome, it can increase breast cancer risk when it’s mutated.
- PTEN: The PTEN gene normally helps regulate cell growth. Inherited mutations in this gene cause Cowden syndrome, a rare disorder in which people are at increased risk for both benign and malignant breast tumors, as well as growths in the digestive tract, thyroid, uterus, and ovaries. Defects in this gene can also cause a different syndrome called Bannayan-Riley-Ruvalcaba syndrome that’s not thought to be linked to breast cancer risk. The syndromes caused by mutations in PTEN can be grouped together as PTEN Tumor Hamartoma Syndrome.
- CDH1: Inherited mutations in this gene cause hereditary diffuse gastric cancer, a syndrome in which people develop a rare type of stomach cancer at an early age. Women with mutations in this gene also have an increased risk of invasive lobular breast cancer.
- STK11: Defects in this gene can lead to Peutz-Jeghers syndrome. People affected with this disorder develop pigmented spots on their lips and in their mouths, polyps in the urinary and gastrointestinal tracts, and have an increased risk of many types of cancer, including breast cancer.
- PALB2: The PALB2 gene makes a protein that interacts with the protein made by the BRCA2 gene. Defects in this gene can lead to an increased risk of breast cancer. It isn’t yet clear if PALB2 gene mutations also increase the risk for ovarian cancer and male breast cancer.
Genetic testing: Genetic testing can be done to look for mutations in the BRCA1 and BRCA2 genes (or less commonly in other genes such as PTEN or TP53). Although testing can be helpful in some situations, the pros and cons need to be considered carefully.
If you are thinking about genetic testing, it’s strongly recommended that first you talk to a genetic counselor, nurse, or doctor qualified to explain and interpret the results of these tests. It’s very important to understand what genetic testing can and can’t tell you, and to carefully weigh the benefits and risks of genetic testing before these tests are done. Testing is expensive and might not be covered by some health insurance plans.
Family history of breast cancer
Breast cancer risk is higher among women whose close blood relatives have this disease.
Having a first-degree relative (mother, sister, or daughter) with breast cancer about doubles a woman’s risk. Having 2 first-degree relatives increases her risk about 3-fold.
Although the exact risk is not known, women with a family history of breast cancer in a father or brother also have an increased risk of breast cancer.
Overall, less than 15% of women with breast cancer have a family member with this disease. This means that most (85%) women who get breast cancer do not have a family history of this disease.
Personal history of breast cancer
A woman with cancer in one breast has an increased risk of developing a new cancer in the other breast or in another part of the same breast. (This is different from a recurrence (return) of the first cancer.) This risk is even higher if breast cancer was diagnosed at a younger age.
Race and ethnicity
Overall, white women are slightly more likely to develop breast cancer than are African-American women, but African-American women are more likely to die of this cancer. In women under 45 years of age, however, breast cancer is more common in African-American women. Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.
Dense breast tissue
Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. A woman is said to have dense breasts (on a mammogram) when she has more glandular and fibrous tissue and less fatty tissue. Women with dense breasts on a mammogram have a risk of breast cancer that is 1.2 to 2 times that of women with average breast density. Unfortunately, dense breast tissue can also make mammograms less accurate.
A number of factors can affect breast density, such as age, menopausal status, the use of certain drugs (including menopausal hormone therapy), pregnancy, and genetics.
Certain benign breast conditions
Women diagnosed with certain benign breast conditions may have an increased risk of breast cancer. Some of these conditions are more closely linked to breast cancer risk than others. Doctors often divide benign breast conditions into 3 general groups, depending on how they affect this risk.
Non-proliferative lesions: These are not associated with overgrowth of breast tissue. They do not seem to affect breast cancer risk, or if they do, it’s to a very small extent. They include:
- Fibrosis and/or simple cysts (sometimes called fibrocystic changes or disease)
- Mild hyperplasia
- Adenosis (non-sclerosing)
- Phyllodes tumor (benign)
- A single papilloma
- Fat necrosis
- Duct ectasia
- Periductal fibrosis
- Squamous and apocrine metaplasia
- Epithelial-related calcifications
- Other benign tumors (such as lipoma, hamartoma, hemangioma, neurofibroma, adenomyoepthelioma)
Mastitis (infection of the breast) is not a lesion, and it doesn’t increase the risk of breast cancer.
Proliferative lesions without atypia: These conditions show excessive growth of cells in the ducts or lobules of the breast tissue. They seem to raise a woman’s risk of breast cancer slightly (1½ to 2 times normal). They include:
- Usual ductal hyperplasia (without atypia)
- Sclerosing adenosis
- Several papillomas (called papillomatosis)
- Radial scar
Proliferative lesions with atypia: In these conditions, there’s excessive growth of cells in the ducts or lobules of the breast tissue, and some of the cells do not look normal. These have a stronger effect on breast cancer risk, raising it about 4 to 5 times higher than normal. These types of lesions include:
- Atypical ductal hyperplasia (ADH)
- Atypical lobular hyperplasia (ALH)
Women with a family history of breast cancer and either hyperplasia or atypical hyperplasia have an even higher risk of developing a breast cancer.
For more information on these conditions, see Non-cancerous Breast Conditions.
Lobular carcinoma in situ
In lobular carcinoma in situ (LCIS), cells that look like cancer cells are growing in the lobules of the milk-producing glands of the breast, but they have not grown through the wall of the lobules. LCIS (also called lobular neoplasia) is sometimes grouped with ductal carcinoma in situ (DCIS) as a non-invasive breast cancer, but it differs from DCIS in that it doesn’t seem to become invasive cancer if it isn’t treated.
Women with LCIS have a 7- to 11-fold increased risk of developing cancer in either breast.
Starting menstruation before age 12
Women who have had more menstrual cycles (periods) because they started menstruating early (before age 12) have a slightly higher risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the hormones estrogen and progesterone.
Going through menopause after age 55
Women who have had more menstrual cycles because they went through menopause later (after age 55) have a slightly higher risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the hormones estrogen and progesterone.
Previous chest radiation
Women who as children or young adults were treated with radiation therapy to the chest area for another cancer (such as Hodgkin disease or non-Hodgkin lymphoma) have an increased breast cancer risk. This varies with the patient’s age when they got radiation. The risk is highest if the radiation was given during adolescence, when the breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk.
Diethylstilbestrol (DES) exposure
From the 1940s through the early 1970s some pregnant women were given DES, an estrogen-like drug, because it was thought to lower their chances of losing the baby (miscarriage). These women have a slightly increased risk of developing breast cancer. Women whose mothers took DES during pregnancy may also have a slightly higher risk of breast cancer. For more information, see DES Exposure: Questions and Answers.
Last Medical Review: 10/09/2015
Last Revised: 10/20/2015