The discrepancies in breast cancer survival rates between white and black women in the United States aren’t just socioeconomic, says a new study published in the Journal of the American Medical Association. New findings suggest African Americans may actually have a genetic predisposition to more aggressive tumors, Fox News reports.

For the study, researchers reviewed nearly 450,000 breast cancers diagnosed in the United States between 2004 and 2011. Overall, 51 percent of white women were diagnosed with early-stage cancers, while only 37 percent of black women caught the disease early on.

After adjusting their data for the time of diagnosis, as well as other factors that are known to affect breast cancer outcomes, such as a patient’s income, researchers noted that survival disparities between the races persisted. That suggested to them that biology might be partly to blame.

Specifically, the findings showed that black women were more likely to die than white women from small tumors with more aggressive characteristics. “We do know that breast cancers in African-American women do tend to be more aggressive than breast cancer in white women,” said Nancy Keating, MD, PhD, a cancer researcher at Brigham and Women’s Hospital. “This—as well as other studies—supports this.”

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