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Risk factors you cannot change
Simply being a woman is the main risk factor for developing breast cancer. Although women have many more breast cells than men, the main reason they develop more breast cancer is because their breast cells are constantly exposed to the growth-promoting effects of the female hormones estrogen and progesterone. Men can develop breast cancer, but this disease is about 100 times more common among women than men.
Your risk of developing breast cancer increases as you get older. About 1 out of 8 invasive breast cancers are found in women younger than 45, while about 2 out of 3 invasive breast cancers are found in women age 55 or older.
Genetic risk factors
About 5% to 10% of breast cancer cases are thought to be hereditary, resulting directly from gene defects (called mutations) inherited from a parent.
BRCA1 and BRCA2:
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. If you have inherited a mutated copy of either gene from a parent, you have a high risk of developing breast cancer during your lifetime.
The risk may be as high as 80% for members of some families with BRCA mutations. These cancers tend to occur in younger women and more often affect both breasts than cancers in women who are not born with one of these gene mutations. Women with these inherited mutations also have an increased risk for developing other cancers, particularly ovarian cancer.
Although in the United States, BRCA mutations are found most often in Jewish women of Ashkenazi (Eastern Europe) origin, they can occur in any racial or ethnic group.
Changes in other genes: Other gene mutations can also lead to inherited breast cancers. These genes mutations are much rarer and often do not increase the risk of breast cancer as much as the BRCA genes. They are not frequent 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 mutated copy of this gene has been linked to a high rate of breast cancer in some families.
If you are considering genetic testing, it is strongly recommended that first you talk to a genetic counselor, nurse, or doctor qualified to explain and interpret the results of these tests. It is 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 may not be covered by some health insurance plans.
•p53: Inherited mutations of the p53 tumor suppressor gene cause the Li-Fraumeni syndrome (named after the 2 researchers who first described it). People with this syndrome have an increased risk of breast cancer, as well as several other cancers such as leukemia, brain tumors, and sarcomas (cancer 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 does not cause this syndrome, it can increase breast cancer risk about twofold when it is 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.
•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.
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 p53). Although testing may be helpful in some situations, the pros and cons need to be considered carefully.
For more information, see the American Cancer Society document, Genetic Testing: What You Need to Know. You may also want to visit the National Cancer Institute Web site (www.cancer.gov/cancertopics/Genetic-Testing-for-Breast-and-Ovarian-Cancer-Risk).
Family history of breast cancer
Women whose close blood relatives have breast cancer have a higher risk for this 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.
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 a 3- to 4-fold 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.
Race and ethnicity
White women are slightly more likely to develop breast cancer than are African-American women. However, African-American women are more likely to die of this cancer. At least part of this seems to be because African-American women tend to have more aggressive tumors, although the reasons for this are not known. Asian, Hispanic, and Native American women have a lower risk of developing and dying from breast cancer.
Dense breast tissue
Women with denser breast tissue (as seen on a mammogram) have more glandular tissue and less fatty tissue, and have a higher risk of breast cancer. Unfortunately, dense breast tissue can also make it harder for doctors to spot problems on mammograms.
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.
These conditions are not associated with overgrowth of breast tissue. They do not seem to affect breast cancer risk, or if they do it is to a very small extent. They include:
•Fibrocystic disease (fibrosis and/or cysts)
Proliferative lesions without atypia:
•Phyllodes tumor (benign)
•A single papilloma
•Mastitis (infection of the breast)
•Other benign tumors (lipoma, hamartoma, hemangioma, neurofibroma)
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 (1 ½ to 2 times normal). They include:
•Usual ductal hyperplasia (without atypia)
Proliferative lesions with atypia:
•Several papillomas or papillomatosis
In these conditions, there is excessive growth of cells in the ducts or lobules of the breast tissue, and the cells no longer appear normal. They have a stronger effect on breast cancer risk, raising it 4 to 5 times higher than normal. They 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 the separate American Cancer Society document, Non-cancerous Breast Conditions.
Lobular carcinoma in situWomen with lobular carcinoma in situ (LCIS) have a 7 -to 11-fold increased risk of developing cancer in either breast.
Women who have had more menstrual cycles because they started menstruating at an early age (before age 12) and/or went through menopause at a later age (after age 55) have a slightly higher risk of breast cancer. This may be related to a higher lifetime exposure to the hormones estrogen and progesterone.
Previous chest radiation
Women who as children or young adults had radiation therapy to the chest area as treatment for another cancer (such as Hodgkin disease or non-Hodgkin lymphoma) are at significantly increased risk for breast cancer. This varies with the patient's age when they got the radiation. If chemotherapy was also given, it may have stopped ovarian hormone production for some time, lowering the risk.. The risk of developing breast cancer from chest radiation 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 an estrogen-like drug called DES 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.
Risk factors you cannot change