Scientists at Duke are studying the causes of breast cancer to learn more about risk factors and ways of preventing this disease.

At present, 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 age 35. Most breast cancers occur in women over 50, and the risk is especially high for women over 60. Also, breast cancer occurs more often in white women than African-American or Asian women.
Risk Factors

Research has shown that the following conditions increase a woman's chances of getting breast cancer; however, most women who develop breast cancer have none of the risk factors listed, other than the risk that comes with growing older.

Risk factors include:

• Personal history of breast cancer.
• 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 (an irregular pattern of cell growth) may increase a woman's risk for developing cancer.
• Genetic alterations. About 5 percent of breast cancers are linked to changes (mutations) in certain genes. Studies show that some breast cancer is linked to changes of the BRCA1 and BRCA2 genes. If a woman has inherited a mutated gene from either parent, she is more likely to develop breast cancer. About 50 to 60 percent of women with these inherited changes will develop breast cancer by the age of 70.
• Estrogen. Evidence suggests that the longer a woman is exposed to estrogen (estrogen made by the body, taken as a drug, or delivered by a patch), the more likely she is to develop breast cancer. For example, the risk is somewhat increased among women who began menstruation 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. Also, women who have their first child late (after about age 30) have a greater chance of developing breast cancer than women who have a child at a younger age.
• Breast density. Breasts that have a high proportion of lobular and ductal tissue appear dense on mammograms. Breast cancers nearly always develop in lobular or ductal tissue (not fatty tissue).
• 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 for developing breast cancer. Studies show that if treatment was received during the period of breast development, the woman has a higher risk for developing breast cancer later in life.
• Alcohol. Some studies suggest a slightly higher risk of breast cancer among women who drink alcohol.