The main risk factors for breast cancer are things you cannot change: being a woman, getting older, and having certain gene changes. These make your risk of breast cancer higher. But having a risk factor, or even many, does not mean that you are sure to get the disease.
Being a woman
Simply being a woman is the main risk factor for breast cancer. Men can have breast cancer, too, but this disease is about 100 times more common in women than in men. This might be because men have less of the female hormones estrogen and progesterone, which can promote breast cancer cell growth.
As you get older, your risk of breast cancer goes up. Most invasive breast cancers (those that have spread from where they started) are found in women age 55 and older.
About 5% to 10% of breast cancer cases are thought to be hereditary, meaning that they result directly from gene defects (called mutations) passed on from a parent.
The most common cause of hereditary breast cancer is an inherited mutation in the BRCA1 and BRCA2 genes. In normal cells, these genes help prevent cancer by making proteins that help keep the cells from growing abnormally. Mutated versions of these genes cannot stop abnormal growth, and that can lead to cancer.
If you have inherited a mutated copy of either gene from a parent, you have a higher risk of breast cancer.
In some families with BRCA1 mutations the lifetime risk of breast cancer is as high as 80%, but 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 are more often found in younger women and more often in both breasts than cancers not linked to these mutations. Women with these inherited mutations also have a higher risk of developing other cancers, mainly 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 anyone can have them.
Changes in other genes
Other gene mutations can also lead to inherited breast cancers. These gene mutations are much less common and most of them do not increase the risk of breast cancer as much as the BRCA genes. They are seldom causes of inherited breast cancer.
•ATM: The ATM gene normally helps repair damaged DNA. Inheriting 2 abnormal copies of this gene 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 gives instructions for making 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 some other cancers such as leukemia, brain tumors, and sarcomas (cancers of bones or connective tissue). This mutation is a rare cause of breast cancer.
•CHEK2: Li-Fraumeni syndrome can also be caused by inherited mutations in the CHEK2 gene. A CHEK2 mutation, even when it doesn’t cause this syndrome, can increase breast cancer risk about 2-fold.
•PTEN: The PTEN gene normally helps regulate cell growth. Inherited mutations in this gene cause Cowden syndrome, a rare disorder that puts people at higher risk for both non-cancer and cancer tumors in the breasts, 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. 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 have pigmented spots on their lips and in their mouths, polyps in the urinary and gastrointestinal tracts, and a higher risk of many types of cancer, including breast cancer.
•PALB2: The PALB2 gene makes a protein that interacts with the protein made by the BRCA2gene. Mutations in this gene can lead to a higher 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 can be done to look for mutations. While testing can be helpful in some cases, the pros and cons need to be considered carefully.
If you’re thinking about genetic testing, it’s strongly recommended that you first talk to a genetic counselor, nurse, or doctor who can 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 costs a lot and might not be covered by some health insurance plans.
Family history of breast cancer
It’s important to note that most women (about 8 out of 10) who get breast cancer do not have a family history of the disease, but:
•Women who have close blood relatives with breast cancer have a higher risk of the disease.
•Having a first-degree relative (mother, sister, or daughter) with breast cancer almost doubles a woman’s risk. Having 2 first-degree relatives increases her risk about 3-fold.
•Women with a father or brother who have had breast cancer also have a higher risk of breast cancer.
Overall, less than 15% of women with breast cancer have a family member with this disease.
A woman with cancer in one breast has a higher risk of developing a new cancer in the other breast or in another part of the same breast. (This is different from a recurrence or return of the first cancer.) This risk is even higher for younger women with breast cancer.
Race and ethnicity
Overall, white women are slightly more likely to develop breast cancer than African-American women, but African-American women are more likely to die of this cancer. In women under age 45, 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. Someone is said to have dense breasts (on a mammogram) when they have more glandular and fibrous tissue and less fatty tissue. Women with dense breasts on 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.
Women diagnosed with certain benign (non-cancer) breast conditions may have a higher 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 conditions don’t 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)
•Phyllodes tumor (benign)
•A single papilloma
•Squamous and apocrine metaplasia
•Other tumors (lipoma, hamartoma, hemangioma, neurofibroma, adenomyoepithelioma)
Mastitis (infection of the breast) is not a tumor and does not increase the risk of breast cancer.
Proliferative lesions without atypia (cell abnormalities): In these conditions there’s excessive growth of cells in the ducts or lobules of the breast. They seem to raise a woman’s risk of breast cancer slightly. They include:
•Usual ductal hyperplasia (without atypia)
•Several papillomas (called papillomatosis)
Proliferative lesions with atypia: In these conditions, the cells in the ducts or lobules of the breast tissue grow excessively, and some of them no longer look normal.. These types of lesions include:
•Atypical ductal hyperplasia (ADH)
•Atypical lobular hyperplasia (ALH)
Breast cancer risk is raised 3½ to 5 times higher than normal in women with these changes. If a woman has a family history of breast cancer and either hyperplasia or atypical hyperplasia, she has an even higher risk of breast cancer.
Starting menstruation (periods) before age 12
Women who have had more menstrual cycles 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 because they have a longer lifetime exposure to the hormones estrogen and progesterone.
Having radiation to your chest
Women who as children or young adults were treated with radiation therapy to the chest for another cancer (such as Hodgkin disease or non-Hodgkin lymphoma) have a significantly higher risk for breast cancer. This varies with the patient’s age when they got radiation. And if you had chemotherapy with the radiation, it might have stopped ovarian hormone production for some time, which lowers the risk. The risk of developing breast cancer from chest radiation is highest if you had radiation during adolescence, when your breasts were still developing. Radiation treatment after age 40 does not seem to increase breast cancer risk.