Triple-negative breast cancers affect people of all races. Breast cancers in African-American women are more likely to be triple-negative than those in white women.
Among African-American women who develop breast cancer, there is an estimated 20 to 40 percent chance of the breast cancer being triple-negative.
Researchers do not yet understand why premenopausal women and women in some ethnic groups have higher rates of triple-negative breast cancer than other groups of women.