Most cases of breast cancer occur in women between the ages of 30 and 80 and about 80% of those cases affect women age 50 and older. So the primary risk factor for breast cancer is simply being a woman, followed by increasing age.

Other risk factors that have been identified, include genetic links to breast cancer. But, it is unclear how many women who are genetically predisposed to having breast cancer ever actually develop the disease. And in other instances, people who seem to have none of the risk factors -- such as men -- develop breast cancer. Women account for 99 percent of breast cancer cases; men account for nearly 1 percent.

Listed below are risk factors associated with breast cancer. Keep in mind though that these risk factors are just "factors." And having one or more of these risk factors does not mean
that you will necessarily develop breast cancer, just that you are at higher risk of developing breast cancer than someone who does not have any of these factors.
 

Age: Both the numbers and the seriousness of breast cancer incidence increase with age. Almost 80% of new cases of breast cancer detected each year are among women over the age of 50.  Race: Caucasian women are more likely to develop breast cancer than are African-American women, but among women under the age of 50, African-American women are at higher risk.    Gender: Breast cancer in men accounts for less than 1% of the overall number of breast cancer cases. However, men should be aware of risk factors in their family history and of signs and symptoms of the disease just like women.

• Genetics: Although family history has long been considered a risk factor for breast cancer, it is now estimated that only about 5%-10% of breast cancers are considered the result of genetic predisposition.  The two breast cancer “susceptibility” genes—BRCA1 and BRCA2—which were discovered in 1994 are estimated to account for 40%-50% of all such cases of hereditary breast cancers. 

• Family history: The primary risk associated with a family history of breast cancer is when there is a “first-degree” relative who has developed the disease – a mother, sister, or daughter. This is especially significant when the individual developed cancer at an early age. Risk is also considered higher for women who have other relatives with the disease, but the risk is not considered as high. Many authorities attribute this risk to similarities in lifestyle combined with a potential familial trait.

• Personal history of breast cancer: A woman who has had breast cancer is at a higher risk for both a recurrence of the original disease and for a new breast cancer than the overall population.

• History of benign breast changes with clinical diagnosis of atypical hyperplasia: For many years it was thought that a woman with benign breast change was at a higher risk of breast cancer. However, many believe that the risk was more related to a higher difficulty of detecting a change in breast tissue than to a genuinely higher risk. Currently, the increased risk is considered to affect those women who have a clinical diagnosis of atypical hyperplasia only.

• Hormonal factors: Breast tissue is affected by a woman’s hormones throughout her reproductive years. And the usual criteria for assessing a higher level of risk for breast cancer are: early onset of menstruation, late onset of menopause, older age at giving birth, and a small number of pregnancies. 

The Study of Tamoxifen and Raloxifene (STAR), one of the largest breast cancer prevention studies ever conducted, is currently recruiting volunteers at more than 400 centers in the United States, Puerto Rico, and Canada. Learn more about the STAR Trial from the National Cancer Institute.