Version May 2024
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INTRODUCTION — Breast cancer is the most commonly diagnosed cancer in women in the United States [1]. However, not all women have the same risk of developing breast cancer during their lifetime. Studies have shown that certain risk factors increase the likelihood that a woman will develop breast cancer.
This topic review discusses the individual factors that increase or decrease your risk of developing breast cancer.
CANCER CARE DURING THE COVID-19 PANDEMIC — COVID-19 stands for "coronavirus disease 2019." It is an infection caused by a virus called SARS-CoV-2. The virus first appeared in late 2019 and has since spread throughout the world. Getting vaccinated lowers the risk of severe illness; experts recommend COVID-19 vaccination for anyone with cancer or a history of cancer.
In some cases, if you live in an area with a lot of cases of COVID-19, your doctor might suggest rescheduling or delaying medical appointments. But this decision must be balanced against the importance of getting care to screen for, monitor, and treat cancer. Your doctor can talk to you about whether to make any changes to your appointment schedule. They can also advise you on what to do if you test positive or were exposed to the virus.
RISK FACTORS — Many risk factors associated with breast cancer cannot be changed, but some can be modified. Having some risk factors does not mean you will definitely get breast cancer; many people with risk factors never develop cancer. Instead, risk factors help to identify people who may benefit most from screening or other preventive measures. It's important to work with your health care provider to understand your personal risk of breast cancer and discuss your options.
It is important to remember that breast cancer can also occur in women who have no identifiable risk factors. The average woman has approximately a 10 to 15 percent chance of developing breast cancer if she lives into her 90s. On the other hand, the risk of developing breast cancer in a woman with a strong family history of the disease who has inherited one of the genes that predispose her to breast cancer is over 50 percent. Even if your personal risk factors suggest that you have a low risk of breast cancer, it's still important to talk to your provider about your options for breast cancer screening. (See "Patient education: Breast cancer screening (Beyond the Basics)".)
STANDARD RISK FACTORS
Increasing age — The primary risk factor for breast cancer in most women is older age. The incidence of breast cancer rises sharply with age until the age of 45 to 50, at which point the rise is less steep. At age 75 to 80, the incidence rates flatten out and then start to decline.
Sex — Breast cancer occurs 100 times more frequently in females than in males. However, males can get breast cancer too.
Race/ethnicity — In the United States, White women have the highest rate of breast cancer; for every 100,000 women, there are 124 cases diagnosed. The rate of breast cancer is lower in Black women (113 per 100,000), American Indians/Alaska natives (92 per 100,000), and Hispanic women (90 per 100,000). It is lowest in Asian Americans/Pacific Islanders (82 per 100,000).
Weight — Weight gain and obesity are associated with an increased risk of breast cancer in women who have been through menopause. A higher body mass index (BMI) is associated with a lower risk of breast cancer in premenopausal women, although the mechanism behind this association is not clear.
Tall stature — Being tall is associated with an increased risk of breast cancer. In studies, women who were at least 69 inches (175 cm) tall were more likely to develop breast cancer compared with women less than 63 inches (160 cm) tall.
Benign breast disease — In addition to breast cancer, women can develop abnormal breast findings. These breast abnormalities can develop because of excessive growth of the glandular breast tissue (also known as proliferative lesions) or can be comprised of increases in fibrous tissue, ductal enlargement, or cyst formations (known as nonproliferative lesions). Women with a history of proliferative breast lesions have an increased risk for breast cancer, particularly if the cells appear abnormal (atypical hyperplasia).
Breast density on mammography — Women whose mammograms show many dense areas of tissue have an increased risk of breast cancer compared with women whose mammograms reveal mainly fat tissue.
High bone density — Women with a high bone mineral density (BMD) have a higher risk of breast cancer. Bone contains estrogen receptors and is sensitive to circulating estrogen. Therefore, BMD may reflect circulating estrogen levels.
Personal history of breast cancer — Women who have already had cancer in one breast have an increased risk of developing cancer in the other breast. If a woman has a prior history of ductal carcinoma in situ (DCIS), this risk is approximately 5 percent over the next 10 years. However, if there is a personal history of an invasive breast cancer, the risk is 1 percent per year for premenopausal women and 0.5 percent per year for postmenopausal women.
Family history — Family history is an important risk factor for breast cancer, although a history of breast cancer involving a first-degree relative (mother, sister, or daughter) is only reported by 20 percent of women with breast cancer. Overall, less than 10 percent of all breast cancers are associated with inherited genetic mutations. For that small group of breast cancers caused by gene mutations, breast cancer susceptibility genes 1 and 2 (BRCA1 and BRCA2) are the most common. For women with a BRCA1 or BRCA2 mutation, the lifetime risk of breast cancer ranges from 45 to 70 percent. Genetic testing for the BRCA mutation is discussed in detail separately. (See "Patient education: Genetic testing for hereditary breast, ovarian, prostate, and pancreatic cancer (Beyond the Basics)".)
Hormonal factors — Having high levels of estrogen is associated with an increase in breast cancer risk.
Menopausal hormone therapy — Long-term use of combined oral estrogen-progestin (eg, for five years or more) to treat symptoms of menopause in women ages 50 to 79 increases the risk of breast cancer as well as heart disease, stroke, and clots in the legs. The risk of breast cancer when estrogen is used alone, without progestin, does not appear to be increased, especially when used for a short time. (See "Patient education: Menopausal hormone therapy (Beyond the Basics)".)
Birth control pills — Unlike oral estrogen-progestin used for menopausal hormone therapy, many studies have documented that oral contraceptives (birth control pills) are not clearly associated with an increased risk of breast cancer.
Fertility medications — Data are still mixed and sparse on the relationship between breast cancer risk and fertility medications, but there does not appear to be an association. In vitro fertilization (IVF) also does not appear to increase a person's risk of breast cancer.
Androgens — Elevated testosterone levels in women are associated with an increased risk of breast cancer, with some studies suggesting an elevated risk specifically for hormone receptor-positive disease.
Reproductive factors
Age at first period and at menopause — Breast cancer risk is increased in women who started menstruating at a younger age (ie, before 13 years) as well as in those who started menopause at an older age. This is likely due to the longer overall exposure to estrogen in a woman's lifetime.
Pregnancy and breastfeeding — Some studies suggest that women who have given birth multiple times are less likely to develop breast cancer later in life than women who have never given birth. However, other studies suggest that this only holds true for women who started having children at a younger age (ie, before 35). Breastfeeding has also been found to be associated with a lower risk of developing breast cancer; the protective effect seems to increase with longer duration of breastfeeding. (See "Patient education: Deciding to breastfeed (Beyond the Basics)", section on 'Why is breastfeeding important?'.)
Abortion is not associated with a risk of breast cancer.
LIFESTYLE FACTORS — A number of modifiable risk factors have been identified that are associated with an increased risk of breast cancer. These include the following:
Physical inactivity — While there is no direct evidence that inactivity is associated with an increased risk of breast cancer, physical exercise appears to protect against breast cancer in both premenopausal and postmenopausal women.
Smoking — Both passive and active tobacco smoking have been associated with an increased risk of breast cancer, especially among premenopausal women. This risk is associated with early initiation, longer duration, and/or higher pack-years of smoking.
DIETARY FACTORS — A number of dietary factors have been reported to increase the risk of breast cancer. Among them, alcohol intake has the strongest association to breast cancer incidence.
Alcohol — There is a significant relationship between alcohol consumption and an increased risk of breast cancer, which begins with alcohol intake as low as three drinks per week. The risk appears to increase with greater alcohol consumption and when combined with the use of menopausal hormone therapy. There does not appear to be a difference by type of alcohol (wine versus beer versus liquor).
Dietary pattern — Some studies have found that eating a low-fat diet reduces the risk of breast cancer. Additionally, a diet that is rich in fruits, vegetables, fish, and olive oil (often called the "Mediterranean diet") may also lower the risk of breast cancer. While the evidence is limited, this type of diet has other health benefits as well.
Red meat and processed meat — There is some evidence that eating a lot of red meat or processed meat may be associated with an increased risk of breast cancer.
Calcium/vitamin D — Diets low in calcium and vitamin D have been associated with an increased breast cancer risk in premenopausal but not in postmenopausal women. However, one study of women who supplemented their diet with vitamin D and calcium did not show a difference in the number of women diagnosed with breast cancer.
Soy/phytoestrogens — Phytoestrogens are naturally occurring plant substances with a chemical structure similar to estrogen. They consist mainly of isoflavones (found in high concentrations in soybeans and other legumes) and lignans (found in a variety of fruits, vegetables, and cereal products). There is low-quality evidence that soy-rich diets in Western women prevent breast cancer. Dietary soy does not appear to increase breast cancer risk.
Caffeine — There is no strong association between caffeine intake and breast cancer risk.
ENVIRONMENTAL FACTORS
Geographic residence — Within the United States, geographic clusters with a high incidence of breast cancer have been described. Although these clusters are most likely due to regional differences in established breast cancer risk factors, studies are ongoing to better understand them.
Exposure to ionizing radiation — Exposure to ionizing radiation of the chest at a young age, as occurs with treatment of Hodgkin lymphoma or in survivors of atomic bomb or nuclear plant accidents, is associated with an increased risk of breast cancer.
Night-shift work — Women who work at night have a higher risk of breast cancer compared with women who do not work night shifts. The primary reason for this remains under study but may be tied to the hormone melatonin, which is normally produced at night.
Phthalates — Phthalates are chemicals found in medical supplies, food containers, cosmetics, toys, and medications. While they have been studied for a potential association with breast cancer risk, the effect is unclear.
Other factors — Organochlorines, including polychlorinated biphenyls (PCBs), dioxins, and organochlorine pesticides such as dichlorodiphenyltrichloroethane (DDT), have been investigated. These compounds are weak estrogens and can stay in a person's system for years. However, an association with breast cancer has not been demonstrated.
In addition, cosmetic breast implants, electromagnetic fields, electric blankets, and hair dyes have not been associated with breast cancer risk.
MEDICATIONS — Several medication classes may have an effect on breast cancer risk, although their association with breast cancer is weak at best.
Nonsteroidal anti-inflammatory drugs — The data are mixed in showing an association between nonsteroidal anti-inflammatory drugs (NSAIDs), which include ibuprofen and naproxen, and breast cancer risk. While some studies show that people who used aspirin or ibuprofen had a lower risk of breast cancer, others have not.
Bisphosphonates — Oral bisphosphonates are a type of drug commonly used for the treatment of osteoporosis and for women with breast cancer with evidence of bone loss attributed to aromatase inhibitors. Whether their use is a true protective factor against breast cancer is unclear.
REDUCING BREAST CANCER RISK — Changes like quitting smoking, cutting back on alcohol, and eating more fruits and vegetables can decrease your chances of developing breast cancer and lead to other health benefits.
In specific cases, health care providers might recommend taking medications or considering surgery to reduce the risk of breast cancer. Your provider can talk to you about your situation and options. (See "Patient education: Medications for the prevention of breast cancer (Beyond the Basics)" and "Patient education: Genetic testing for hereditary breast, ovarian, prostate, and pancreatic cancer (Beyond the Basics)", section on 'Risk-reducing options'.)
Although screening mammography does not reduce the risk of developing breast cancer, screening significantly decreases the risk of dying from breast cancer. The goal of screening is to detect cancer at an early stage, when it can be treated. When to start screening, and how often to be screened, depends on your personal risk factors and preferences. (See "Patient education: Breast cancer screening (Beyond the Basics)".)
ESTIMATING YOUR RISK — Although breast cancer risk assessment tools are available and can be found online, there are limitations to their usefulness. This is partly because not all important risks have been identified, and partly because most risk factors for breast cancer are relatively weak and common in the population. The best way to assess and understand your personal risk is to speak with a health care provider and discuss your options for screening. (See "Patient education: Breast cancer screening (Beyond the Basics)".)
WHERE TO GET MORE INFORMATION — Your health care provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients as well as selected articles written for health care professionals are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient education: Breast cancer (The Basics)
Patient education: Breast cancer screening (The Basics)
Patient education: Common breast problems (The Basics)
Patient education: Genetic testing for breast, ovarian, prostate, and pancreatic cancer (The Basics)
Patient education: Ductal carcinoma in situ (DCIS) (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient education: Breast cancer screening (Beyond the Basics)
Patient education: Genetic testing for hereditary breast, ovarian, prostate, and pancreatic cancer (Beyond the Basics)
Patient education: Medications for the prevention of breast cancer (Beyond the Basics)
Patient education: Menopausal hormone therapy (Beyond the Basics)
Patient education: Risks and benefits of alcohol (Beyond the Basics)
Patient education: Non-estrogen treatments for menopausal symptoms (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Factors that modify breast cancer risk in women
Breast imaging for cancer screening: Mammography and ultrasonography
Clinical manifestations, differential diagnosis, and clinical evaluation of a palpable breast mass
Genetic testing and management of individuals at risk of hereditary breast and ovarian cancer syndromes
Cancer risks and management of BRCA1/2 carriers without cancer
Overview of hereditary breast and ovarian cancer syndromes
Screening for breast cancer: Strategies and recommendations
The following organizations also provide reliable health information.
●National Cancer Institute
1-800-4-CANCER
●People Living With Cancer: The official patient information website of the American Society of Clinical Oncology
(www.cancer.net/portal/site/patient)
●American Cancer Society
1-800-ACS-2345
●National Library of Medicine
(www.nlm.nih.gov/medlineplus/healthtopics.html)
●Susan G. Komen Breast Cancer Foundation
ACKNOWLEDGMENT — The editorial staff at UpToDate would like to acknowledge Wendy Y Chen, MD, MPH, who contributed to an earlier version of this topic review.
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