Racial Differences Likely In Cancer Risks
Why is cancer more deadly for African-Americans and Hispanics than for white Americans?
That old question is getting new answers from a radical new approach sponsored by the American Association for Cancer Research (AACR). The first harvest from this new approach is on display this week in Atlanta at the first Science of Cancer Health Disparities conference.
"This is not about documenting disparity, it is about tackling the problem," conference co-chair Olufunmilayo I. Olopade, M.D., director of the University of Chicago's center for clinical cancer genetics, said at a news conference. "We hope this is the first of many meetings, so we can report on success in reducing disparity, not on the fact that it exists."
Until now, most disparity research has focused on people's behavior or on their physical and social environments. It's time to break out of these "silos," says conference co-chairman Timothy R. Rebbeck, Ph.D., professor of biostatistics and epidemiology at the University of Pennsylvania.
"The goal of meeting is to bring together biology, genetics, and all the underlying basic science related to cancer disparities," Rebbeck said at the news conference. "The answers are not going come just from studies of genes or of the environment, but from studying all these things together."
Studies presented at the conference show that progress already is being made.
Breast Cancer Genes Work Differently In African-Americans
When an American woman of European descent gets breast cancer, her odds of survival are significantly better than an African-American woman who gets the same cancer.
Most observers have written this disparity off to African-American women's relatively poorer access to health care. But recent studies that account for health care access, income, and other social factors still find that African-American women are more likely to die when they get breast cancer.
This led National Cancer Institute researcher Damali N. Martin, Ph.D., MPH, and colleagues to take a closer look at breast cancer samples from African-American women. Martin reported the study results in a conference presentation.
In the first part of their study, the researchers found that African-American women's breast tumors tended to have more blood vessels than tumors from white American women.
Tumors from African-American women were also surrounded by more of the immune cells called tumor macrophages. Instead of helping, tumor macrophages give off chemical signals that promote the growth of cancer-feeding blood vessels.
Were the tumors in African-American women really different? To find out, Martin and colleagues next looked at what the tumor-cell genes were doing. In a pilot study of tumor genes from 18 African-American women and 17 white American women, they found that the tumors from African-American women were much more active in promoting growth of tumor blood vessels.
"This indicates to us that genes involved in blood vessel development and immune system function may play a role in the tumors we see in African-American women," Martin tells WebMD.
Different Ethnicity, Different Colon Cancer Risk
It's well known that people in different countries are at different risk of colon cancer. Studies suggest dietary factors have a lot to do with this, but diet alone cannot account for these differences.
A crucial genetic difference seems to play a role, suggests a study presented to the conference by Mary A. Garza, Ph.D., MPH, deputy director of the Center for Minority Health at the University of Pittsburgh.
Garza focused on a gene that controls the body's ability to use folate, a nutrient needed to produce and maintain new cells.
Most people have the "CC" variant of this gene - that is, they inherited two copies of a gene that makes a folate-maintaining enzyme more active. People with the mixed "CT" verson of the gene have 35 percent less enzyme activity; those with the "TT" version have 70 percent less enzyme activity.
Garza expected to find that people with the TT version of the gene were more likely to get colon cancer. But among people of Asian descent, people with the TT gene were significantly less likely to get colon cancer than those with the CC version.
On the other hand, Latinos who inherited the mixed CT gene variant were 20 percent more likely to get colon cancer than those with the CC version, although there were too few Latinos in the sample for this finding to reach statistical significance.
Why is this happening? So far, there's no good explanation.
"We need more studies to tease this apart," Garza tells WebMD. "And this brings up the issue of African-Americans and Latinos when it comes to research. We have made progress, but sometimes all the samples we have to work with are from Caucasians. We need more minority participation in these clinical trials."
By Daniel DeNoon
Reviewed by Louise Chang
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