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April 16, 2008 (San Diego) -- Genetics may help explain why prostate and breast cancers are more deadly in African-Americans than in whites, researchers say.
Much of this discrepancy has been attributed to socioeconomic factors such as access to screening and adequate cancer care, says Tiffany Wallace, PhD, of the National Cancer Institute.
"But there's been a missing link, which turns out to be genetic factors," she tells WebMD.
African-American men are more likely to develop prostate cancer than white men, and over two times more likely to die from the disease, according to the American Cancer Society.
To determine what role genetics plays, Wallace and colleagues compared prostate tumors that had been removed from 33 African-Americans and 36 white men. Standard gene-chip technology was used to examine the samples.
Results showed that the activity of 162 genes was different between the two groups.
Wallace says that genes that suppress the immune system were more likely to be overactive in African-American men. A weakened immune system doesn't recognize tumor cells as foreign invaders that need to be quashed. This allows cancer cells to grow and spread.
Other genes that were overexpressed in African-Americans are involved in the production of interferon, a substance that helps combat infection with viruses.
That finding raises the intriguing possibility that African-American men are being infected with an unidentified prostate-cancer-causing virus, Wallace says.
The research was presented at the annual meeting of the American Association for Cancer Research.
Genetic differences may also help explain a well-known paradox in cancer care: African-American women have a lower risk of developing breast cancer than whites but a higher risk of dying from it.
African-American women are 36% more likely to die from breast cancer than white women, according to the American Cancer Society.
African-American women are more likely to develop large and aggressive tumors that are notoriously difficult to treat, says Lori Field, PhD, of the Windber Research Institute in Windber, Pa.
Field and colleagues examined breast tumor samples from 26 African-Americans and 26 whites.
All the women were being treated at the Walter Reed Army Medical Center in Washington, D.C., because they or a family member were in the military. That's important because it minimizes the chance the unequal access to care would affect the results.
The activity of 65 genes was different between the two groups. Twenty-eight of the genes, many of which are involved in cell division, growth, and spread, were overactive in African-American women.
The other 37 genes were underactive in the African-Americans. Many of those genes are involved in curbing the growth and spread of cancer, Field says.
Olufunmilayo I. Olopade, MD, director of the Center for Clinical Cancer Genetics at the University of Chicago Medical Center, says that both genes and environment determine whether a person of any race will get cancer. Olopade moderated a news conference to discuss the findings.
"Your genes are altered by your life and environment, so it's always changing as a function of what you eat, where you live, and what you do. You can't say X amount of the problem is due to access and X amount is due to genetics. You have to look at the whole picture," Olopade tells WebMD.
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