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Topic Overview

Although the exact cause of breast cancer is not known, most experts agree that there are several factors that increase your risk of breast cancer.

Top risk factors linked to breast cancer

Aging. Your risk of breast cancer increases as you get older. By age group, breast cancer is diagnosed in:⁷

• 4 out of 1,000 women in their 30s.
• 14 out of 1,000 women in their 40s.
• 26 out of 1,000 women in their 50s.
• 37 out of 1,000 women in their 60s.

Being female. Although breast cancer can occur in men, most breast cancer is found in women.

Conditions that increase the risk of developing breast cancer

Personal history of breast cancer. Women who have had breast cancer in one breast have an increased chance of having another breast cancer. The breast cancer can come back in the same breast, in the opposite breast, or in other areas of the body, such as the lungs, liver, brain, or bones.

Family history. A woman's risk of breast cancer increases if her mother, sister, daughter, or two or more other close relatives, such as cousins, have a history of breast cancer, especially if they were diagnosed with breast cancer before age 50.

• Women who inherit specific changes (genetic mutations) in the BRCA1 and BRCA2 genes are much more likely to have breast cancer. They are also more likely to have colon or ovarian cancer. But most women who have a family history of breast cancer do not have changes in BRCA genes.
• Mutations in the BRCA1 and BRCA2 genes are more common in certain ethnic groups, such as Ashkenazi Jews.³
• Genetic tests are available to determine whether you have the genetic mutations long before any cancer appears. In families where many women have had breast or ovarian cancer, genetic testing can show whether a woman has specific genetic changes known to greatly increase the risk of breast cancer. Doctors may suggest ways to try to prevent or delay breast cancer or to improve the detection of breast cancer in women who have the genetic mutations.

Breast changes. Women who have atypical hyperplasia, ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS) or who have had two or more breast biopsies for other noncancerous conditions are more likely to have breast cancer.

Other factors that increase the risk of breast cancer

Race. In the United States, breast cancer occurs more frequently in white women than in black, Hispanic, or Asian women. But black women are more likely to get breast cancer at a younger age and are also more likely to die of breast cancer.⁵ This may be linked in part to genetic differences—an aggressive type of breast cancer called basal-like tumor seems most likely to affect young African-American women. Lower survival rates among black women may also be linked to lower-quality health care.²

Radiation therapy. Women whose breasts were exposed to significant amounts of radiation at a young age, especially those who were treated for Hodgkin's lymphoma, have an increased risk for developing breast cancer. Studies show that the younger a woman was when she received her treatment, the higher her risk for developing breast cancer later in life.⁵

Late or no 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. Women who never had children have an increased risk for developing breast cancer.

Not breast-feeding. Women who don't breast-feed have a higher risk of breast cancer than those who breast-feed. The more months of breast-feeding, the lower the breast cancer risk.

Hormones. Female hormones play a part in some types of breast cancer.

• The use of hormone therapy after menopause for more than 4 years causes an increased risk of developing breast cancer.⁴ This increased risk occurs with current use of hormones and returns to normal over time after hormones are stopped.⁶
• Beginning menstruation before age 12 and beginning menopause later than age 55 increase a woman's risk of breast cancer. The years you have a menstrual cycle are your high-estrogen years. Experts think that the longer you have higher estrogen, the more risk you have for breast cancer.¹
• Having extra body fat and drinking alcohol both lead to higher levels of estrogen in the body. Especially after menopause, when your estrogen levels are naturally low, this raises your breast cancer risk.¹

For more information about your personal risk level, go to www.cancer.gov/bcrisktool.

In most cases, experts cannot explain why a woman develops breast cancer. Studies show that most women who develop the disease do not have any of the risk factors listed above, other than the risk that comes with growing older. Also, most women with known risk factors, except for BRCA mutations, do not develop breast cancer. Research continues into the causes of breast cancer to learn more about risk factors and ways of preventing this disease.