Study Finds Breast Tumors More Aggressive in African-American Women Than in White Women

August 26, 2004

For more than four decades, statistics have shown that African-American women are less likely to get breast cancer than white women but are more likely to die of the disease.

Researchers have been hunting for reasons to explain this discrepancy in mortality. And now, for the first time, they have uncovered a piece of the puzzle that shows genetics may play a role.

Researchers report in the August issue of the online edition of the journal Cancer that the tumors of African-American women are nearly four times more likely to have a genetic mutation related to a more aggressive form of breast cancer than are the tumors of white women.

The study, "African American/White Differences in Breast Carcinoma," was led by Beth Jones, PhD, an epidemiologist at the Yale University School of Medicine.

Jones and colleagues studied tumor tissue that had been taken from 145 African-American women and 177 white women who had been diagnosed with breast cancer between 1987 and 1989. All of the women had been interviewed and asked an array of questions about their health for a previous study.

The researchers analyzed the tumors to see if there were genetic differences between the cancers African-American and white women developed. They looked for alterations in three specific genes: HER-2/neu-a gene that can make cancer more aggressive; p53-a tumor-suppressor gene; and c-met-a gene that can be an indicator that metastases has occurred.

The study found that African-American women were more likely to have tumors that had alterations in the p53 tumor suppressor gene (Twenty-eight (24.5%) of the African-American women had tumors that were p53-positive compared with 9 (7.1%) of the white women.) This is significant because mutations in the p53 gene are associated with poorer outcomes, possibly because the mutations make chemotherapy less effective. No differences were seen between the two groups in the number of tumors that were HER-2 positive or c-met positive.

Like previous studies, this study found that African-American women were more likely than white women to be diagnosed with later stage breast cancer, to have larger tumors, and to have had their cancer spread to their lymph nodes. The African-American women were also more likely to have Grade 3 tumors (the grade refers to how abnormal the cells appear), and tumors that were hormone-negative. (The study found that 53 (46.5%) of the African-American women had tumors that were estrogen-receptor (ER)-positive compared with 79 (61.2%) of the white women; 35 (31%) of the African-American women had tumors that were progesterone receptor (PR)-positive compared with 48 (37.5%) of the white women.) As the researchers note, "this is the first population-based investigation to report that there are significant differences between African-American and white women with regard to the prevalence of tumors that overexpress p53." These findings, they continue, are "consistent with the emerging literature showing that African-American women are more likely than white women to be diagnosed with aggressive tumors."

Susan says:

We have known for some time that African-American women are more likely to die of breast cancer than are white women. But we haven't been able to figure out why.

Many theories have been proposed: socioeconomic factors, lack of access to health care, lack of access to mammography screening, and genetic or biological differences between the races. Research into all of these areas is helping us to better understand the reasons why this is occurring - and what can be done about it.

Claims that genetic differences could be the reason behind the disparity in death rates have generated much controversy. And while we may find that genetics does play a role, the problem with attributing the discrepancy solely to genetic or biological differences between the races is that people of different races are more similar genetically than they are different.

In some respects this study shows this to be true. The study did indeed find a difference between the two groups of women: 28 (24.5%) of the African-American women had tumors that were p53-positive compared with 9 (7.1%) of the white women. Yet, the study also showed that most of the women, regardless of their race, did not have tumors that were p-53 positive. Thus, race does tell us something about who might have a tumor that is p-53 positive. But it's not the whole story.

The findings from this study appear to support the idea of testing breast cancer tumors - all women's tumors, not just African-American women's tumors - to determine if they are p-53 positive. The problem comes when we try to determine how we would use that information. When a woman's tumor is HER-2 positive, it tells us Herceptin may be a treatment option. When a woman's tumor is hormone-positive, it tells us hormone therapy is likely to be effective. But, right now, we don't have any drugs that are specifically used to treat tumors that are p-53 positive. In time, we may. But right now, knowing a tumor is p-53 positive tells us only that a tumor is more aggressive, not how to best treat it.

References:

Jones BA, Kasi SV, Howe CL, et al. African American/White Differences in Breast Carcinoma: p53 and Other Tumor Characteristics. Cancer. 2004;101. Published online on August 9, 2004. To appear in the print issue September 15, 2004.