Risk Factors for Breast Cancer

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A wide variety of factors may influence an individual's likelihood of developing various types of cancer. These factors are usually referred to as risk factors. Different types of cancer may have different risk factors.

Some factors that influence cancer risk, such as dietary and exercise habits, are modifiable. By changing these aspects of their lifestyle, people may reduce their risk of cancer. Other factors that influence risk, such as age, gender, or family history, cannot be modified. Traditionally, it was thought that little could be done about these risk factors. However, it is now possible for individuals who are at high risk of some types of cancer because of non-modifiable risk factors to reduce their chances of getting the disease through special measures such as chemoprevention or preventive surgery. Additionally, knowledge of risk factors can be useful when considering the benefits of early detection methods for breast cancer, including X-ray mammography, clinical breast examination, and breast self-examination.

Many possible risk factors for breast cancer have been proposed. Compelling scientific evidence supports the importance of some of these factors. These factors are referred to as "established" risk factors. Other proposed risk factors have more limited support; the evidence for their role is inconclusive. These risk factors can be described as "speculated." Still other factors have little or no scientific support. They are primarily myths and misconceptions and are best described as "unsupported."

The established risk factors for breast cancer are female gender, age, previous breast cancer, benign breast disease, hereditary factors (family history of breast cancer), early age at menarche (first menstrual period), late age at menopause, late age at first full-term pregnancy, postmenopausal obesity, low physical activity, and high-dose exposure to ionizing radiation early in life.

Speculated risk factors for breast cancer include never having been pregnant, having only one pregnancy rather than many, not breast feeding after pregnancy, use of postmenopausal estrogen replacement therapy or postmenopausal hormone (estrogen/progestin) replacement therapy, use of oral contraceptives, prescribed diethylstilbestrol (DES), certain specific dietary practices (high intake of fat and low intakes of fiber, fruits, and vegetables), alcohol consumption, tobacco smoking, abortion, breast augmentation, low intake of phytoestrogens (estrogens from plant sources), and non-use of nonsteroidal anti-inflammatory drugs (NSAIDs).

There is only limited evidence in support of the possibility that xenoestrogens (synthetic estrogens) and large breast size might increase breast cancer risk. Unsupported risk factors include premenopausal obesity, exposure to low-dose ionizing radiation in midlife, high intake of phytoestrogens, electromagnetic fields, breast trauma, and the use of antiperspirants.

For all women, ACSH recommends the following.

1. Discuss your risk factors for breast cancer with your physician.

2. Stay active and watch your weight.

3. Be sure to have mammograms and breast examinations as often as your doctor recommends.

Kathleen Meister, M.S., is a freelance medical writer and former ACSH research associate. John Morgan, Dr.P.H., is an Associate Professor of Public Health and Preventive Medicine at Loma Linda Linda University and is the cancer epidemiologist for Region 5 of the California Cancer Registry. His interests include cancer control and prevention, and epidemiologic research.

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Risk Factors for Breast Cancer