Breast Cancer
Causes & Risk Factors
The risk of breast cancer increases gradually as a woman gets older. Breast cancer is uncommon in women under the age of 35 and women age 40 and older are at risk. Most breast cancers occur in women over the age of 50. The risk is especially high for women over age 60. This disease is very uncommon before menopause.
Research has shown that the following conditions place a woman at increased risk for breast cancer:
Personal History of Breast Cancer Women who have had breast cancer face an increased risk of getting breast cancer again. A woman who has had breast cancer in one breast has an increased risk of getting this disease in her other breast.
Genetic Alterations Changes in certain genes (BRCA1, BRCA2, and others) increase the risk of breast cancer. In families in which many women have had the disease, genetic testing can sometimes show the presence of specific genetic changes. Health care providers may suggest ways to try to reduce the risk of breast cancer, or to improve the detection of this disease in women who have these changes in their genes.
Family History of Breast Cancer A woman's risk of breast cancer is higher if her mother, sister, or daughter had breast cancer, especially at a young age (before age 40). Having other relatives with breast cancer on either her mother's or her father's side of the family may also increase a woman's risk.
Certain Breast Changes Some women have cells in the breast that look abnormal under a microscope. Having certain types of abnormal cells (atypical hyperplasia or lobular carcinoma in situ [LCIS]) increases the risk of breast cancer.
Other factors associated with an increased risk for breast cancer include:
Taking DES (diethylstilbestrol) DES is a synthetic form of estrogen that was given to some pregnant women in the United States between about 1940 and 1971. (DES is no longer given to pregnant women.) Women who took DES during pregnancy have a slightly increased risk of getting breast cancer. This does not yet appear to be the case for their daughters who were exposed to DES before birth. However, as these daughters grow older, more studies of their breast cancer risk are needed.
Breast Density Women age 45 and older whose mammograms show at least 75 percent dense tissue are at increased risk. Dense breasts contain many glands and ligaments, which makes breast tumors difficult to "see," and the dense tissue itself is associated with an increased chance of developing breast cancer.
Radiation Therapy Women whose breasts were exposed to radiation during their childhood, especially those who were treated with radiation for Hodgkin's disease, are at an increased risk for developing breast cancer throughout their lives. Studies show that the younger a woman was when she received her treatment, the higher her risk for developing breast cancer later in life.
Late Childbearing Women who had their first child after the age of 30 have a greater chance of developing breast cancer than women who had their children at a younger age.
Race Breast cancer occurs more often in white women than Latina, Asian, or African American women.
Being Obese After Menopause After menopause, women who are obese have an increased risk of developing breast cancer. Being obese means that the woman has an abnormally high proportion of body fat. Because the body makes some of its estrogen (a hormone) in fatty tissue, obese women are more likely than thin women to have higher levels of estrogen in their bodies. High levels of estrogen may be the reason that obese women have an increased risk of breast cancer. Also, some studies show that gaining weight after menopause increases the risk of breast cancer.
Physical Inactivity Women who are physically inactive throughout life appear to have an increased risk of breast cancer. Being physically active may help to reduce risk by preventing weight gain and obesity.
Alcoholic Beverages Some studies suggest that the more alcoholic beverages a woman drinks, the greater her risk of breast cancer.
Also at a somewhat increased risk for developing breast cancer are women who started menstruating at an early age (before age 12), experienced menopause late (after age 55), never had children, or took menopausal hormone therapy (either estrogen alone or estrogen plus progestin) for 5 or more years. Each of these factors increases the amount of time a woman's body is exposed to estrogen. The longer this exposure, the more likely she is to develop breast cancer. Much research has been done to learn whether having an abortion or a miscarriage affects a woman's chance of developing breast cancer later on. Large, well-designed studies have consistently shown no link between abortion or miscarriage and the development of breast cancer.
In most cases, doctors cannot explain why a woman develops breast cancer. Studies show that most women who develop breast cancer have none of the risk factors listed above, other than the risk that comes with growing older. Also, most women with known risk factors do not get breast cancer. Scientists are conducting research into the causes of breast cancer to learn more about risk factors and ways of preventing this disease.