Oncologist-approved cancer information from the American Society of Clinical Oncology
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Breast Cancer

This section has been reviewed and approved by the Cancer.Net Editorial Board, 1/2013
Risk Factors


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. However, knowing your risk factors and talking about them with your doctor may help you make more informed lifestyle and health care choices.

Most women who develop breast cancer have no obvious risk factors and no family history of breast cancer. This means that all women need to be aware of changes in their breasts and talk with their doctors about receiving regular clinical breast examinations (an examination of the breast by a doctor) and mammograms (x-ray of the breast that can detect a tumor that is too small to be felt). It is likely that more than one risk factor influences the development of breast cancer.

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 one breast has a 1% to 2% chance per year of developing a second breast cancer in her opposite breast, if she has no other risk factors.

Family history of breast cancer. Women who have a first-degree relative (mother, sister, daughter) diagnosed with breast cancer have an increased risk of the disease. Having more than one first-degree relative with breast cancer further increases that risk, especially if the cancer was diagnosed at a younger age or in a man, because it may be a sign of genetic changes that are inherited (see below). Women who have a second-degree relative (aunt, niece, grandmother, granddaughter) diagnosed with breast cancer also have a higher risk of breast cancer. The father’s (paternal) side of the family should also be considered and has the same effect as the mother’s (maternal) side when evaluating family history. For example, you may be at higher risk if your father’s sister or mother had breast cancer.

Genetic predisposition. Mutations (changes) to the breast cancer genes 1 or 2 (BRCA1 or BRCA2) are linked to an increased breast and ovarian cancer risk. Blood tests (genetic testing) are available to test for known mutations in these genes, but are not recommended for everyone and are recommended only after a person has received appropriate genetic counseling. Men may also carry these gene mutations. Breast or ovarian cancer on the paternal side of the family greatly increases the risk of having hereditary breast and ovarian cancer. Researchers estimate that about 5% to 10% of all breast cancers in the United States are linked to inherited genetic mutations, such as the BRCA1, BRCA2, and other genes. If a woman learns she has one of these genetic mutations, there are steps she can take to lower her risk of breast and ovarian cancers, and 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. BRCA1 and BRCA2 genetic mutations cancer also increase a man’s risk of breast cancer, as well as the risk for other cancers. Learn more about the genetics of breast cancer.

Personal history of ovarian cancer. A history of ovarian cancer can increase a woman’s risk of breast cancer, if the ovarian cancer was because of an inherited mutation. Breast cancer gene mutations, such as BRCA1 or BRCA2, greatly increase the risk of both ovarian and breast cancers.

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 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 protect against breast cancer because it pushes breast cells into their final phase of maturation. Breastfeeding may also help lower the risk of developing breast cancer before menopause.

Postmenopausal hormone replacement therapy. Recent use (within the past five years) and long-term use (several years or more) of postmenopausal (after menopause) hormone therapy with both estrogen and progesterone increases a woman’s risk of breast cancer. In fact, the number of new breast cancers diagnosed has been dropping as fewer women have been taking postmenopausal hormone therapy. However, women who have taken estrogen alone (those who have had their uterus removed for other reasons) for up to five years appear to have a slightly lower risk of breast cancer.

Oral contraceptives (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 overall, although the disease is diagnosed more often in young black women than in young white women. Although white women are more likely to develop breast cancer, black women are more likely to die from the disease. Reasons for survival differences are unclear and probably involve both biologic and socioeconomic factors. Women of Ashkenazi Jewish heritage also have an increased risk of breast cancer because they are also more likely to have BRCA gene mutations. 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. Breast cancer diagnoses have been increasing in second generation Asian/Pacific islander and Hispanic women for unclear reasons, but likely related to changes in diet and lifestyle.

Atypical hyperplasia of the breast. This diagnosis increases the risk of developing breast cancer in the future and is characterized by abnormal, but not cancerous, cells found in a biopsy of the breast.

LCIS. As explained in the Overview section, this diagnosis refers to abnormal cells found in the lobules or glands of the breast. LCIS in one breast increases the risk of developing invasive breast cancer (cancer that spreads into surrounding tissues) in either breast in the future. If LCIS is found during a biopsy (see Diagnosis), it may be removed to check for other changes, and 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, and they 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 one to two 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.

Radiation. High doses of ionizing radiation (such as from tanning booths and x-rays) may increase a woman’s risk of breast cancer. Radiation to the chest given at a young age, such as that given for treatment for a childhood cancer, also increases the risk of breast cancer. However, 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 tumors on standard imaging tests, such as a mammography (see Diagnosis). Breast density may be from higher levels of estrogen, rather than a separate risk factor, and usually decreases with age. Researchers are looking at whether lowering breast density might also decrease the risk of breast cancer.

© 2005-2014 American Society of Clinical Oncology (ASCO). All rights reserved worldwide.

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