Risk factors for breast cancer

Patient information: Risk factors for breast cancer

Author
Suzanne W Fletcher, MD
Section Editor
Daniel F Hayes, MD
Deputy Editor
Don S Dizon, MD, FACP

Disclosures

INTRODUCTION — About 210,000 women in the United States are diagnosed with breast cancer each year. However, not all women have the same risk of developing breast cancer during their lifetime. Studies have shown that certain factors, called risk factors, increase the likelihood that a woman will develop breast cancer. Many of these risk factors are not reversible, but some can be modified.

Not all factors increase a woman’s chance of developing breast cancer equally. Some factors (such as inheriting a breast cancer-related gene) increase a woman’s risk of breast cancer more than others (see ‘Strong risk factors’ below).

The presence of breast cancer risk factors does not mean that cancer is inevitable: many women with risk factors never develop breast cancer. Instead, risk factors help to identify women who may benefit most from screening or other preventive measures. Individual women should work with their clinicians to determine their own personal risk of breast cancer, based upon their own circumstances.

It is important to remember that breast cancer can also occur in women who have no identifiable risk factors. The average woman has about 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. All women should discuss guidelines for breast cancer screening with their clinicians, even if they have a low risk for breast cancer based upon their risk factor profile.

This topic review discusses the individual factors that increase a woman’s risk of developing breast cancer and also reviews those factors that are thought to protect against the development of breast cancer.

STRONG RISK FACTORS — Unlike lung cancer, for which smoking is the biggest and most powerful risk factor, there is no single factor that is responsible for the majority of breast cancers in women. Nevertheless, there are three factors that strongly increase a woman’s risk of developing this disease: advancing age, family history of the disease, and a personal history of breast cancer.

Increasing age — The primary risk factor for breast cancer in most women is older age. Overall, 85 percent of cases occur in women 50 years of age and older, while only 5 percent of breast cancers develop in women younger than age 40. Most North American expert groups suggest that women over age 50 be screened for breast cancer every year. Breast cancer screening of women in their 40s and over the age of 70 is controversial. (See “Patient information: Breast cancer screening”.)

Family history — Women who have a family history of breast or ovarian cancer are at a higher risk for breast cancer than those who lack such a history. Women who have an especially strong family history (eg, two or more first-degree relatives [a mother, daughter, or sister] with breast or ovarian cancer, particularly before menopause) have a greater than 50 percent chance of developing breast cancer. This represents an approximately five- to 10-fold increase in a woman’s baseline risk of developing breast cancer.

One of the main factors responsible for this elevated risk is an inherited genetic mutation in one of two genes, called BRCA1 and BRCA2. Genetic testing for the BRCA mutation is discussed in detail elsewhere. (See “Patient information: Genetic testing for breast and ovarian cancer”.)

Previous breast cancer — Women who have had cancer in one breast have an increased risk of developing cancer in the other breast. This is especially true if a woman has an inherited BRCA mutation. This fact underscores the need for close surveillance after treatment of a breast cancer, particularly in a woman who has inherited a BRCA mutation.

MODERATE RISK FACTORS — Five factors can modestly increase a woman’s risk of developing breast cancer (with the presence of each factor increasing the relative risk by 1.5- to 2-fold):

Density of the breasts on mammogram — Women whose mammograms show many dense areas of tissue have an increased risk of breast cancer compared to women whose mammograms reveal mainly fat tissue. A woman who is told that her mammogram has areas of increased density should ask her healthcare provider to explain what this means.

Biopsy abnormalities — Women who have had a prior breast biopsy that revealed a proliferative abnormality (excessive growth of the glandular breast tissue, also called hyperplasia) have an increased risk for breast cancer, particularly if the cells appear abnormal (atypical hyperplasia). Otherwise, benign breast conditions that are not proliferative (eg, fibrocystic change, or a noncomplex fibroadenoma) do not increase the risk of a woman developing breast cancer. Any woman who undergoes a biopsy of a breast abnormality needs to fully understand the results, particularly if they impact the frequency of breast cancer screening.

Exposure to radiation — Women who have undergone high-dose radiation therapy to the chest region, usually as part of cancer treatment, have an increased risk for breast cancer compared to women who have never had radiation therapy.

OTHER RISK FACTORS — Several other factors can increase a woman’s risk of developing breast cancer. Many of these factors are related to exposure to a hormone, estrogen. None are very powerful risk factors.

Age at time of reproductive events — During a woman’s reproductive years, estrogen stimulates cells of the breast’s glandular tissue to divide. The longer a woman is exposed to estrogen, the greater her risk for breast cancer. Estrogen exposure is increased if a woman began menstruating at or before 11 years of age, or if she experiences menopause at age 55 years or older.

Pregnancy and breastfeeding — Women who have never given birth are more likely to develop breast cancer after menopause than women who have given birth multiple times. The timing of a first pregnancy also appears to play a role; women who have their first full-term pregnancy at the age of 30 years or older have an increased risk of breast cancer as compared to women who give birth before age 30.

Hormone replacement therapy (HRT) — As a woman ages, the breast’s glandular tissue, the tissue in which breast cancer arises, is gradually replaced by fat. HRT includes estrogen, which slows or reverses this process. A large clinical trial has found that long-term use of combined estrogen-progestin (approximately five years) in women ages 50 to 79 increases a woman’s 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 does not appear to be increased, especially when used for a short time. (See “Patient information: Postmenopausal hormone therapy”.)

Each woman should discuss the pros and cons of this therapy with her clinician before deciding if it is right for her. Alternatives to estrogen therapy may be preferable for some women, while others may choose to use estrogen for some period of time.

Weight — Obese women are more likely than thin women to develop breast cancer after menopause.

Alcohol — Women who drink alcohol have an increased risk of breast cancer, perhaps due to elevated levels of estrogen in the body. The more alcohol a woman drinks, the greater her risk. However, moderate alcohol intake may protect against other diseases. There is evidence that women can protect themselves against the alcohol-breast cancer link by consuming an adequate amount of folic acid with a daily multivitamin and by eating leafy green vegetables. Women should discuss the benefits and risks of alcohol consumption with their healthcare provider. (See “Patient information: Risks and benefits of alcohol”.)

Presence of other cancers — Women who have been diagnosed with cancer of the endometrium, ovary, or colon are more likely to develop breast cancer than women who do not have these cancers.

Miscellaneous factors — Several other factors are linked to breast cancer risk for reasons that are unknown. Women of high socioeconomic status are more likely than women of low socioeconomic status to develop breast cancer, and women who live in urban settings are more likely than women who live in rural settings to develop breast cancer. Some studies support an association between exposure to light at night (such as with night shift work) and the risk of breast cancer, but the strength of the association has been variable.

Race/ethnicity and religion also appear to play a role in breast cancer risk. Black women are more likely than Asian women to develop breast cancer before the age of 40 years, whereas White (non-Hispanic) women are more likely than Asian women to develop breast cancer at the age of 40 years and older. Women who smoke also appear to have an increased risk of breast cancer.

DECREASING THE RISK — Several factors can decrease the risk of breast cancer.

Removal of the ovaries — Women whose ovaries have been removed before age 35 are at lower risk of breast cancer later in life compared to women who have ovaries. However, removal of the ovaries places women at higher risk for more common diseases such as coronary heart disease and osteoporosis, and oophorectomy is not recommended for breast cancer prevention in most women; women with the BRCA1 or BRCA2 gene mutation may be encouraged to have their ovaries removed. (See “Patient information: Genetic testing for breast and ovarian cancer”.)

Lifestyle changes — A number of lifestyle changes may reduce breast cancer risk:

Minimize the use of postmenopausal hormones. Consider non-estrogen alternatives (eg, bisphosphonates for treatment of osteoporosis rather than hormones) (see “Patient information: Nonhormonal treatments for menopausal symptoms”).
Although this may not necessarily be a lifestyle choice, having a first child at an earlier age may decrease risk.
Breast feeding for at least 12 months can decrease breast cancer risk.
Avoiding adult weight gain and maintaining a healthy weight may reduce postmenopausal breast cancer risk.
Limiting alcohol may also reduce risk. For those who drink, adding the vitamin folic acid to the diet may reduce this increased risk.
Regular physical activity may also decrease risk.
Medication — Women who are already at higher than average risk can significantly lower their risk of developing breast cancer by taking tamoxifen, raloxifene, or an aromatase inhibitor, such as exemestane, for five years. This is discussed separately. (See “Patient information: Medications for the prevention of breast cancer”.)

Early detection — Even if breast cancer incidence cannot be substantially reduced for some women who are at high risk for developing the disease, the risk of death from breast cancer can be reduced with regular mammography screening. (See “Patient information: Breast cancer screening”.)

ESTIMATING RISK — Many factors can affect a woman’s risk for breast cancer. The relative importance of each of these factors can be confusing.

In most cases, a woman and her clinician can use the Breast Cancer Risk Assessment Tool, which was developed by the National Cancer Institute to estimate personal risk. Calculation of the score entails multiplying a woman’s baseline risk (based upon her age and race/ethnicity) and the risks associated with five key factors. The individual’s risk is compared with a woman the same age who has an “average risk” of developing breast cancer. The tool can be accessed online at www.cancer.gov/bcrisktool/.

WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem.

 

Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.

Patient Level Information:

Patient information: Breast cancer screening
Patient information: Genetic testing for breast and ovarian cancer
Patient information: Medications for the prevention of breast cancer
Patient information: Postmenopausal hormone therapy
Patient information: Risks and benefits of alcohol
Patient information: Nonhormonal treatments for menopausal symptoms

Professional Level Information:

Epidemiology and risk factors for breast cancer
Breast imaging: Mammography and ultrasonography
Breast lumps and other common breast problems
Genetic counseling for individuals at risk for hereditary breast and ovarian cancer syndromes
Genetic testing for hereditary breast and ovarian cancer syndrome
Management of hereditary breast and ovarian cancer syndrome and patients with BRCA mutations
Characteristics of hereditary breast and ovarian cancer syndromes
Screening for breast cancer

The following organizations also provide reliable health information.

National Cancer Institute
1-800-4-CANCER
(www.nci.nih.gov)

People Living With Cancer: The official patient information website of the American Society of Clinical Oncology
(www.cancer.net/portal/site/patient)

National Comprehensive Cancer Network
(www.nccn.com)

American Cancer Society
1-800-ACS-2345
(www.cancer.org)

National Library of Medicine
(www.nlm.nih.gov/medlineplus/healthtopics.html)

Susan G. Komen Breast Cancer Foundation
(www.komen.org)

REFERENCES
Hulka BS, Stark AT. Breast cancer: cause and prevention. Lancet 1995; 346:883.
Olsen O, Gøtzsche PC. Cochrane review on screening for breast cancer with mammography. Lancet 2001; 358:1340.
Freedman DA, Petitti DB, Robins JM. On the efficacy of screening for breast cancer. Int J Epidemiol 2004; 33:43.
National Cancer Institute. Breast Cancer (PDQ®): Screening. Available at: cancer.gov/cancertopics/pdq/screening/breast/healthprofessional (Accessed November 21, 2005).
Kösters JP, Gøtzsche PC. Regular self-examination or clinical examination for early detection of breast cancer. Cochrane Database Syst Rev 2003; :CD003373.