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The exact causes of breast cancer are not known. However, studies show that the
risk of breast cancer increases as a woman gets older. This disease is very uncommon
in women under the age of 35. Most breast cancers occur in women over the age
of 50; the risk is especially high for women over age 60. Also, breast cancer
occurs more frequently in white women than African American or Asian women.
Research has shown that the following conditions increase a woman's chances of getting breast cancer:
Personal history of breast cancer. Women who have had breast cancer in one breast face an increased risk of getting breast cancer in their other breast.
Family history. A woman's risk for developing breast cancer increases if her mother, sister, or daughter had breast cancer, especially at a young age.
Certain breast changes. Having a diagnosis of atypical hyperplasia or lobular carcinoma in situ (LCIS) may increase a woman's risk for developing cancer.
Genetic alterations. Changes in certain genes (BRCA1, BRCA2, and others) increase the risk of breast cancer. Where there is a family history, gene testing can sometimes identify the presence of specific genetic changes. Doctors may then suggest ways to try to delay or prevent breast cancer, or to improve detection.
Other factors associated with an increased risk for breast cancer include:
Estrogen. Evidence suggests that the longer a woman is exposed to estrogen (produced by the body, taken as a drug, or delivered by patch), the more likely she is to develop breast cancer. For example, the risk is somewhat increased among women who began menstruating at an early age (before age 12), experienced menopause late (after age 55), never had children, or took hormone replacement therapy for long periods of time. Each of these factors increases the amount of time a woman's body is exposed to estrogen.
In addition, women who took DES (diethylstilbestrol, a synthetic form of estrogen that was used between the early 1940s and 1971 to prevent miscarriage) are at a slightly higher risk for breast cancer. This does not appear to be the case for their daughters who were exposed to DES in utero. However, more studies are needed as these daughters enter the age range when breast cancer is more common.
Late childbearing. Women who have their first child after about age 30 are at greater risk.
Breast density. Breast cancers nearly always develop in lobular or ductal tissue -- dense tissue -- rather than in breasts with a lot of fatty tissue. In addition, when breasts are dense, it is more difficult for doctors to see abnormal areas on a mammogram.
Radiation therapy. Women whose breasts were exposed to radiation during radiation therapy before age 30, especially those who were treated with radiation for Hodgkin's disease, are at an increased risk. Studies show that the younger a woman was when she received her treatment, the higher her risk for developing breast cancer later in life.
Alcohol. Some studies suggest a slightly higher risk of breast cancer among women who drink alcohol.
However, most women who develop breast cancer have none of the risk factors listed above, other than the risk that comes with growing older. Scientists are still conducting research into the causes of breast cancer to learn more about risk factors and ways of preventing the disease.
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