Breast Cancer: Risk Factors and Prevention

Approved by the Cancer.Net Editorial Board, 04/2017

ON THIS PAGE: You will find out more about the factors that increase the chance of developing this type of cancer. Use the menu to see other pages.

A risk factor is anything that increases a person’s chance of developing cancer. Although risk factors often influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. Knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.

Most breast cancers are sporadic, meaning they develop from damage to a person’s genes that occurs by chance after they are born. There is no risk of passing this gene on to a person's children.

Inherited breast cancers are less common, making up 5% to 10% of cancers. Inherited breast cancer occurs when gene changes called mutations are passed down within a family from 1 generation to the next (see below). Many of those mutations are in tumor suppression genes, such as BRCA1 or BRCA2. These genes normally keep cells from growing out of control and turning into cancer. But when these cells have a mutation, they can grow out of control.

When considering your breast cancer risk, it is important to remember that most women who develop breast cancer have no obvious risk factors and no family history of breast cancer. Multiple risk factors influence the development of breast cancer. This means that all women need to be aware of changes in their breasts. They also need to talk with their doctors about receiving regular breast examinations by a doctor and mammograms, which are x-rays of the breast that can often detect a tumor that is too small to be felt.

The following factors may raise a woman’s risk of developing breast cancer:

  • Age. The risk of developing breast cancer increases as a woman ages, with most cancers developing in women older than 50.

  • Personal history of breast cancer. A woman who has had breast cancer in 1 breast has a higher risk of developing a new cancer in either breast.

  • Family history of breast cancer. Breast cancer may run in the family if your family has 1 or more of the following characteristics:

    • First-degree relatives, such as mothers, sisters, and children, who have been diagnosed with breast cancer or ovarian cancer, especially before age 50. If 2 first-degree relatives developed breast cancer, the risk is 5 times the average risk.

    • Many close relatives who have been diagnosed with breast cancer or ovarian cancer, especially before age 50. Close relatives include grandparents, aunts and uncles, nieces and nephews, grandchildren, and cousins.

    • A family member who developed breast cancer in both breasts.

    • A male relative who developed breast cancer. It is uncertain how much a woman's risk of breast cancer is increased when a man in the family has breast cancer, unless this is due to an inherited mutation.

    If a man within your family has developed breast cancer or a woman has developed breast cancer at an early age or has developed ovarian cancer, it is important to talk with your doctor. Either could be a sign that your family carries an inherited breast cancer genetic mutation, such as BRCA1 or BRCA2 (see Inherited risk/Genetic disposition below).

    When looking at family history, it’s also important to consider your father’s side of the family. Your father’s side is equally important as your mother’s side in determining your personal risk for developing breast cancer.

  • Inherited risk/Genetic predisposition. There are several inherited genes linked with an increased risk of breast cancer, as well as other types of cancer. BRCA1 or BRCA2 are the most common known mutations. Mutations in these genes are linked to an increased risk of breast and ovarian cancers, as well as other types of cancer. A man’s risk of breast cancer, as well as the risk for prostate cancer, is also increased if he has mutations in these genes. Learn more about hereditary breast and ovarian cancer in a 1-page fact sheet (available as a PDF) or in a more detailed guide.

    Other gene mutations or hereditary conditions can increase a person’s risk of breast cancer. They are far less common than BRCA1 or BRCA2, and do not increase the risk of breast cancer as much.

    There are also other genes that may cause an increased risk of breast cancer. More research is needed to understand how they increase a person’s risk. For example, a person can inherit a gene mutation but not develop breast cancer. Research is also ongoing to find other genes that may affect breast cancer risk.

    Genetic testing through blood tests is available to test for known mutations in BRCA1 and BRCA2 genes and other hereditary syndromes. Your doctor may recommend a test called a “panel test.” A panel test looks for mutations in several different genes at the same time. There are different panel tests your doctor can recommend. However, these tests are not recommended for everyone and are recommended only after a person has received appropriate genetic counseling.

    If a woman learns she has a genetic mutation, there may be steps she can take to lower her risk of breast and ovarian cancers. She may need a different breast cancer screening schedule than the general population, such as having tests more often or starting screening at a younger age.

  • Personal history of ovarian cancer. BRCA1 and BRCA2 gene mutations greatly increase the risk of both ovarian and breast cancers. Therefore, women diagnosed with hereditary ovarian cancer caused by a BRCA gene mutation have an increased risk of breast cancer as well. Women with breast cancer who did not inherit a BRCA1 or BRCA2 mutation are generally not at increased risk of ovarian cancer.

  • Estrogen and progesterone exposure. Estrogen and progesterone are hormones in women that control the development of secondary sex characteristics, such as breast development, and pregnancy. A woman’s production of estrogen and progesterone decreases with age, with a steep decrease around menopause. Long-term exposure to these hormones increases breast cancer risk.

    • Women who began menstruating before ages 11 or 12 or went through menopause after age 55 have a somewhat higher risk of breast cancer. This is because their breast cells have been exposed to estrogen and progesterone for a longer time.

    • Women who had their first pregnancy after age 35 or who have never had a full-term pregnancy have a higher risk of breast cancer. Pregnancy may help protect against breast cancer because it pushes breast cells into their final phase of maturation.

  • Hormone replacement therapy after menopause. Using hormone therapy with both estrogen and progestin after menopause, often called postmenopausal hormone therapy or replacement, within the past 5 years or for several years increases a woman’s risk of breast cancer. In fact, the number of new breast cancers diagnosed has dropped substantially as fewer women have been taking postmenopausal hormone therapy. However, women who have taken estrogen alone, without previously receiving progestin, for up to 5 years (because they have had their uterus removed for other reasons) appear to have a slightly lower risk of breast cancer.

  • Oral contraceptives or birth control pills. Some studies suggest that oral contraceptives slightly increase the risk of breast cancer, while others have shown no link between the use of oral contraceptives to prevent pregnancy and development of breast cancer. Research on this topic is ongoing.

  • Race and ethnicity. Breast cancer is the most common cancer diagnosis in women, other than skin cancer, regardless of race. White women are more likely to develop breast cancer than black women, but among women younger than 45, the disease is more common in black women than in white women. Black women are also more likely to die from the disease. Reasons for survival differences include differences in biology, other health conditions, and socioeconomic factors affecting access to medical care.

    Women of Ashkenazi or Eastern European Jewish heritage also have an increased risk of breast cancer because they may be more likely to have inherited a BRCA gene mutation. Breast cancer is least commonly diagnosed in Hispanic, Asian/Pacific Islander, and American Indian/Alaska Native women. Both black and Hispanic women are more likely to be diagnosed with larger tumors and later-stage cancer than white women. However, Hispanic women generally have better survival rates than white women. Breast cancer diagnoses have been increasing in second generation Asian/Pacific Islander and Hispanic women for unclear reasons. However, the increase is likely related to changes in diet and lifestyle associated with living in the United States.

  • Atypical hyperplasia of the breast. This diagnosis increases the risk of developing breast cancer in the future. It is characterized by abnormal, but not cancerous, cells found in a biopsy (see Diagnosis) of the breast.

  • LCIS. As explained in the Introduction section, this diagnosis refers to abnormal cells found in the lobules or glands of the breast. LCIS in 1 breast increases the risk of developing invasive breast cancer in either breast in the future. If LCIS is found during a biopsy (see Diagnosis), it may be removed to check for other changes. Additional treatment may be recommended. Talk with your doctor about the best way to monitor this condition.

  • Lifestyle factors. As with other types of cancer, studies continue to show that various lifestyle factors may contribute to the development of breast cancer.

    • Weight. Recent studies have shown that postmenopausal women who are overweight or obese have an increased risk of breast cancer. These women also have a higher risk of having the cancer come back after treatment.

    • Physical activity. Increased physical activity is associated with a decreased risk of developing breast cancer and a lower risk of having the cancer come back after treatment. Regular physical activity may protect against breast cancer by helping women maintain a healthy body weight, lowering hormone levels, or causing changes in a women’s metabolism or immune factors.

    • Alcohol. Current research suggests that having more than 1 to 2 alcoholic drinks, including beer, wine, and spirits, per day raises the risk of breast cancer, as well as the risk of having the cancer come back after treatment.

    • Food. There is no reliable research that confirms that eating or avoiding specific foods reduces the risk of developing breast cancer or having the cancer come back after treatment. However, eating more fruits and vegetables and fewer animal fats is linked with many health benefits.

  • Socioeconomic factors. More affluent women in all race and ethnic groups have a higher risk of developing breast cancer than less affluent women in the same groups. The reasons for this difference are not known. But these differences may be due to variations in diet, environmental exposures, and other risk factors such as breast density. Women living in poverty are more likely to be diagnosed at an advanced stage and are less likely to survive the disease than more affluent women. This is likely due to multiple factors, including lifestyle factors, other health conditions such as obesity, and tumor biology. Access to health care and a range of treatment options play additional roles.

  • Radiation. Exposure to ionizing radiation at a young age may increase a woman’s risk of breast cancer. For example, therapeutic radiation to the chest for Hodgkin lymphoma may increase breast cancer risk.

    The very small amount of radiation a woman receives during a yearly mammogram has not been linked to an increased risk of breast cancer.

  • Breast density. Dense breast tissue may make it more difficult to find a tumor on standard imaging tests, such as mammography (see Diagnosis). Breast density may be from higher levels of estrogen, rather than a separate risk factor, and usually decreases with age. Some states require that mammogram results include information about breast density if the results show that a woman has dense breast tissue. Researchers are looking at whether lowering breast density might also decrease the risk of breast cancer.

Understanding your risk of breast cancer

Several breast cancer risk assessment tools have been developed to help a woman estimate her chance of developing breast cancer. The best studied is the Gail model, which is available on the National Cancer Institute’s website at www.cancer.gov/bcrisktool. After you enter some personal and family information, including race/ethnicity, the tool provides you with a 5-year and lifetime estimate of the risk of developing invasive breast cancer. Because it only asks for information about breast cancer in first-degree family members and does not include their age at diagnosis, the tool works best at estimating risk in women without a strong inherited breast cancer risk. For some women, other ways of determining the risk of breast cancer may work better. For example, women with an inherited breast cancer risk may consider talking to a genetic counselor.

It is important to talk with your doctor about how to find out your personal risk of breast cancer and to discuss risk-reducing or prevention options (see below).

Prevention

Different factors cause different types of cancer. Researchers continue to look into what factors cause breast cancer. Although there is no proven way to completely prevent this disease, you may be able to lower your risk. Talk with your doctor for more information about your personal risk of breast cancer.

  • Mastectomy. For women with BRCA1 or BRCA2 genetic mutations, which substantially increase the risk for breast cancer, the preventive removal of the breasts may be considered. The procedure, called a prophylactic mastectomy, appears to reduce the risk of developing breast cancer by at least 95%. Women with these mutations should also consider the preventive removal of the ovaries and fallopian tubes, called a prophylactic salpingo-oophorectomy. This procedure can reduce the risk of developing ovarian cancer, as well as breast cancer, by stopping the ovaries from making estrogen. Talk with your doctor about possible physical and emotional side effects when considering having these procedures.

  • Chemoprevention. Women who have a higher risk of developing breast cancer may consider chemoprevention. Chemoprevention is the use of hormone-blocking drugs to reduce cancer risk. The drugs, tamoxifen (Nolvadex, Soltamox) and raloxifene (Evista), are approved by the U.S. Food and Drug Administration (FDA) to lower breast cancer risk. These drugs are called selective estrogen receptor modulators (SERMs) and are not chemotherapy. A SERM is a medication that blocks estrogen receptors in some tissues and not others. Postmenopausal women and premenopausal women may take tamoxifen. Raloxifene is only approved for postmenopausal women. Each drug also has different side effects. Talk with your doctor about whether you may benefit from chemoprevention for breast cancer.

    Aromatase inhibitors (AIs) are also being looked at to reduce breast cancer risk. AIs are a type of hormone-blocking treatment that reduces the amount of estrogen in a woman's body by stopping tissues and organs other than the ovaries from producing estrogen. For example, an AI called exemestane (Aromasin) has shown promise in reducing breast cancer risk. However, AIs can only be used by women who have gone through menopause. Exemestane is not yet approved by the FDA for lowering breast cancer risk in women who do not have the disease. Read more about drugs to reduce breast cancer risk.

    Other drugs being looked at to reduce breast cancer risk include statins, which lower cholesterol, and metformin (multiple brand names), a drug commonly used for diabetes.

  • Lifestyle choices. One way to lower your risk of breast cancer includes getting regular physical activity. Studies suggest that 30 to 60 minutes per day of moderate- to high-intensity physical activity is associated with a lower breast cancer risk. Other ways include staying at a healthy weight, limiting the amount of alcohol you drink, and avoiding the use of post-menopausal hormone therapy to ease menopause symptoms. Breastfeeding may also reduce a woman’s breast cancer risk. Learn about more lifestyle choices that may help lower your risk of breast cancer.

The next section in this guide is Screening. It explains how tests may find early breast cancer before signs or symptoms appear. You may use the menu to choose a different section to read in this guide.