Breast Cancer: Risk Factors and Prevention

Approved by the Cancer.Net Editorial Board, 07/2019

ON THIS PAGE: You will find out more about the factors that increase the chance of developing breast 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 parent to child. 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, it can cause them to 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. A mammogram is an x-ray 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 in any of these situations:

  • 1 or more women are diagnosed at age 45 or younger

  • 1 or more women are diagnosed with breast cancer before age 50 with an additional family history of cancer, such as prostate cancer, melanoma, and pancreatic cancer

  • There are breast and/or ovarian cancers in multiple generations on the same side of the family, such as having both a grandmother and an aunt on the father’s side both diagnosed with these cancers

  • A woman is diagnosed with a second breast cancer in the same or the other breast or has both breast and ovarian cancer

  • A male relative is diagnosed with breast cancer

  • There is a history of breast cancer, ovarian cancer, prostate cancer, and/or pancreatic cancer on the same side of the family

  • Having Ashkenazi Jewish ancestry

It is important to talk with your doctor if your family has experienced any of the above situations. It 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 and other cancers, 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 on this website.

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 genes linked with 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 (see Prevention, below). She may need a different breast cancer screening schedule than the general population, such as having tests more often, starting screening at a younger age, or having different types of screening tests.

Personal history of ovarian cancer. BRCA1 and BRCA2 gene mutations strongly increase the risk of ovarian cancer and breast cancer. 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 generally do not have a higher risk of ovarian cancer.

Early menstruation and late menopause. 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. 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. Longer exposure to these hormones increases breast cancer risk.

Timing of pregnancy. 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 hormone 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 only estrogen, 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 may 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. LCIS refers to abnormal cells found in the lobules or glands of the breast. It is not considered cancer. However, 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.

Breast density. Dense breast tissue may make it more difficult to find a tumor on standard imaging tests, such as mammography (see Diagnosis). Having dense breast tissue generally means you have more milk glands, milk ducts, and supportive tissue in the breast than fatty tissue. 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.

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. Decreased physical activity is associated with an increased risk of developing breast cancer and a higher 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 racial 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 and other health conditions such as obesity and tumor biology. Access to health care and the availability of treatment play additional roles.

Radiation exposure at a young age. 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 mammogram has not been linked to an increased 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 a family history of 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, including ways to prevent it. Although there is no proven way to completely prevent this disease, you may be able to lower your risk.

The following options may help reduce your risk of breast cancer. Talk with your health care team for more information about your personal risk of breast cancer.

Surgery to lower cancer risk

For women with BRCA1 or BRCA2 genetic mutations, which substantially increase the risk of breast cancer, 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, and possibly 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.

Drugs to lower cancer risk (Updated as of 09/2019)

Women who have a higher than usual risk of developing breast cancer can consider talking with their doctor about drugs that may help prevent breast cancer. This approach is called “endocrine prevention” or "chemoprevention." For breast cancer, this is the use of hormone-blocking drugs to reduce cancer risk.

  • Tamoxifen (available as a generic drug) is a type of drug called a selective estrogen receptor modulator (SERM). It is often used as a treatment for breast cancer for women who already have the disease. Tamoxifen blocks the effects of estrogen on tumor growth.

    Tamoxifen may be an option to help lower the risk of breast cancer, specifically ER-positive breast cancer for women who are age 35 or older. Research has shown that it may also be effective to reduce the risk of breast cancer and cause fewer side effects for women with carcinoma in situ or a precancerous breast condition called atypical hyperplasia of the breast. It is not recommended for women with a history of blood clots, stroke, or who are immobilized (unable to move around) for a long time. It is also not recommended for women who are pregnant or who may become pregnant or who are breastfeeding.

    The side effects of tamoxifen may include hot flashes, vaginal discharge, sexual side effects, mood changes, and a higher risk of developing uterine cancer, blood clots, and stroke.

  • Raloxifene (Evista) is also a SERM. It is often used to prevent osteoporosis (thinning of the bones) for women who have gone through menopause.

    Raloxifene may be an option for women age 35 or older who have a higher risk of breast cancer and who have been through menopause. Raloxifene can be used for longer than 5 years and may reduce the risk of bone loss in addition to lowering breast cancer risk. It is not recommended for women who have not been through menopause or who have a history of blood clots, stroke, or are immobilized for a long time.

    The side effects of raloxifene may include hot flashes, leg cramps, swelling of the legs and arms, weight gain, stroke, blood clots, vaginal dryness, and pain during sexual intercourse. Women taking raloxifene are less likely to develop blood clots, uterine problems, and cataracts than women taking tamoxifen.

  • Aromatase inhibitors (AI). AIs reduce the amount of estrogen in a woman's body by blocking estrogen production. There are 2 AIs that may be options for lowering breast cancer risk: exemestane (Aromasin) and anastrozole (Arimidex). AIs can be used as an alternative to tamoxifen for women who have a higher risk of breast cancer and who have been through menopause. AIs are not recommended for women who have not been through menopause and are not usually recommended for women who have osteoporosis.

    The side effects of AIs may include hot flashes, fatigue, difficulty sleeping, diarrhea, joint and muscle pain, vaginal dryness, and bone loss.

This information is based on ASCO recommendations for the Use of Endocrine Therapy for Breast Cancer Risk Reduction. Please note that this link take you to another ASCO website.

Lifestyle choices to lower cancer risk

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. Use the menu to choose a different section to read in this guide.