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:²

• 4 out of 1,000 women in their 30s.
• 15 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.⁹
• 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. For more information, see:

  Should I have a gene test for breast cancer?

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.¹⁰ 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.¹¹