Risk Factors for Breast Cancer
The most important risk factors for breast cancer are:
- Being a woman
Over 70 percent of women who develop the disease have only these two risk factors. The risk of breast cancer increases as a woman gets older. This is even more important after the age of 50. Most breast cancers are found in women 55 and older.
Other factors are known to increase the risk of breast cancer. These fall under two major categories:
- Those that cause moderately higher risk
- Those that cause a slightly higher risk
Not all of the risk factors have the same level of risk. Having one or more doesn’t guarantee that the disease will occur.
BRCA1 and BRCA2 are known as the breast cancer genes. Changes in these genes cause a higher risk of breast and other cancers. These changes can result in an 80 percent chance of developing breast cancer over a lifetime. Changes in other genes, such as p53, PTEN and CHEK2, also increase the risk of breast cancer.
Get more information on genetic risk, counseling and testing. This includes options to help prevent breast cancer for women known to be at high risk.
High-Dose Radiation Exposure
Radiation therapy is used to treat a number of conditions. RT treatment can raise the risk of breast cancer. Risk factors linked to radiation therapy include:
- Exposure to a large amount of radiation before age 30 as treatment for cancers such as lymphoma
Prior Breast Cancer Diagnosis
If you had breast cancer before, you have an increased risk of breast cancer returning. This risk may be three to four times higher than for women with no history of breast cancer.
Direct Family History
Your risk of breast cancer increases if your mother, sister or daughter ("first-degree" relative) has been diagnosed with the condition. If you have two first-degree relatives with breast cancer, your risk increases. The risk is greater if your relatives developed breast cancer before menopause or had cancer in both breasts. Having a male blood relative with breast cancer also increases a woman’s risk of the disease.
87 percent of women with breast cancer have no direct family history of the disease. This means all women should be aware of other risk factors and screening guidelines. A direct family history does not guarantee that you will get breast cancer.
High-Risk Breast Lesions
If you have a history of certain noncancerous (benign) conditions, there is an increased risk of breast cancer. These conditions include:
- Changes in breast cells (breast atypia)
- Lobular carcinoma in situ
Women with a history of these conditions are four to five times more likely to develop breast cancer. Women with either condition are offered more frequent breast cancer screening. This includes:
- Breast exams twice each year
- MRIs in addition to yearly mammograms
An oral medication to lower estrogen may be used to lower your cancer risk. These medicines are tamoxifen and raloxifene.
Maintaining a healthy body weight is important for lowering your risk of breast cancer. Carrying extra weight increases the risk for breast and other cancers. Extra weight means:
- Overweight — body mass index higher than 25
- Obese — body mass index higher than 30
This is particularly important for women after menopause.
Certain body types can also have a higher risk. For example, women who carry more fat in the waist area (apple-shaped). Losing weight is an important step to lowering your breast cancer risk.
Distant Family History
Breast cancer in more distant relatives can slightly raise your breast cancer risk. These may include aunts, grandmothers and cousins. This risk is not nearly as high as when the cancer is found in a first-degree relative.
Hormone Replacement Therapy (HRT)
Long-term use of estrogen and progesterone raises the risk of breast cancer. These hormones are used as hormone replacement therapy, or HRT. The level of risk returns to normal after stopping HRT for five years or more.
Previous Benign Breast Biopsy
Women who had a biopsy showing any of the following have a slightly higher risk:
- Solid, noncancerous breast tumors (fibroadenomas) with complex features
- Hyperplasia without atypia
- Sclerosing adenosis
Early Menstruation and Late Menopause
Women who began menstruating before age 12 are at a higher risk. Women who went through menopause after the age of 55 face a slightly higher risk.
Delayed Childbirth or Not Having Children
Having your first child after age 35 or never having children puts you at slightly higher risk. The reason may be because you are exposed to more estrogen and progesterone over your lifetime.
Drinking more than seven alcoholic drinks a week has been linked to a higher risk of breast cancer. This is particularly true for women under age 30. Women who drink more than one alcoholic drink a day have a slight increase in risk. Those who consume two to five drinks each day have about 1.5 times the risk of women who drink no alcohol. For these women, reducing alcohol intake can help to lower the risk.
Dense breast tissue may slightly increase the risk for breast cancer. Dense tissue can also make the cancer more difficult to detect on mammograms.
The insulin resistance associated with diabetes is believed to raise the risk of breast cancer.
An inactive lifestyle, particularly before age 40, may increase your breast cancer risk. Regular exercise can reduce the risk.
Exposure to some chemicals and pesticides may increase the risk for cancer in general. The level of this risk is not well understood.
Other Cancer in the Family
A family history of certain cancers may increase the risk of breast cancer. This includes cancer of the:
Women descended from Eastern and Central European Jews (Ashkenazi) may be at higher risk. This is because changes in BRCA1 and BRCA2 genes are more common in this population
Changes in the BRCA genes are also more common in certain other ethnic groups. This includes French Canadians and those from Iceland.
Caucasian women are at a slightly higher risk of developing breast cancer. However, women of color (African-American and Latino, for example) under 40 are more likely to develop breast cancer than Caucasian women under 40.
Factors That May Lower Breast Cancer Risk
- Pregnancy before age 35
- Early onset of menopause
- Surgical removal of the ovaries before age 37
Factors Not Linked to Breast Cancer
- Coffee or caffeine consumption
- Underwire bras
- Abortion or miscarriage
- Breast implants
Risk Factors Under Investigation
Research is still being done to determine if certain chemicals increase the risk of breast cancer. Women who use hormone birth control may have a very small rise in their risk of breast cancer. This risk disappears if birth control is stopped for 10 years or more. Other studies show no link between breast cancer and birth control.
Eating foods high in soy may increase breast cancer risk. This is because soy contains natural estrogens. Other studies suggest higher levels of soy in the diet may lower breast cancer risk. Some studies suggest that green tea may lower breast cancer risk.
More research is needed to confirm these findings.
Breast Cancer in African-American and Hispanic Women
Breast cancer among African-American and Hispanic women may be lower than Caucasian women. However, a higher number of African-American and Hispanic women develop breast cancer before age 50.
African-American and Hispanic women diagnosed with breast cancer are more likely to die from their disease. This is partly because they have fewer screening mammograms than white women. This means they are more likely to be diagnosed with cancer at a later stage. At later stages, treatment is more difficult and survival rates are lower.
The difference also reflects a tendency for these populations to have more aggressive types of breast cancer. This can include triple-negative breast cancer which isn’t linked to estrogen, progesterone or HER2-neu.
Breast Cancer in Men
Male breast cancer is relatively rare, with about 1,600 cases diagnosed in the United States each year. Men with breast cancer are typically diagnosed at a later age than women (average age of diagnosis is 65).
A man’s risk of developing breast cancer increases with age. Additional risk factors include:
- Family history of breast cancer (male or female)
- Inherited changes in certain genes
- Conditions that cause higher estrogen in the body
- Radiation exposure to the chest
- Drinking a lot of alcohol
- Liver disease
- Estrogen use