Researchers at the Yale School of Medicine (search) have concluded that black women are four times more likely than white women to have a genetic mutation that makes their breast cancer more deadly.

The new study says that while black women are less likely than white women to get breast cancer, they have a greater chance of developing aggressive tumors.

There has been debate about whether breast cancer differences between blacks and whites are due to socio-economic status, health care or diet.

Beth A. Jones (search), an assistant professor of epidemiology and public health at Yale, said the study shows that race is clearly a factor in whether a tumor will be aggressive.

Data for the study was collected from 145 black women and 177 white women who had breast cancer. Changes in a tumor suppressor gene (search) called p53 were analyzed. Mutations in the p53 gene have been implicated in the onset of about 50 percent of all cancers and are associated with poorer outcomes in breast cancer patients.

The study said that when variables such as income were controlled, African-American women were more likely to have mutations of the p53 gene than white women. Black women also tended to get their tumors at an earlier age than white women.

"The picture now coming down is that the tumors that do occur can be more aggressive in African-Americans," Jones said. "The implications are that early detection is very important, and African-Americans need to be particularly vigilant."

The study, published Monday in the online edition of the journal Cancer, will appear in the journal's Sept. 15 issue.