Are Racial Disparities in Cancer Survival Rates Due to Biological Factors?

July 09, 2009 06:30 PM
by Denis Cummings
A study determines that socioeconomic and cultural factors alone cannot explain the difference in the survival rate of black and white cancer patients, suggesting that biological or genetic factors may be at play.

Blacks With Gender-Related Cancer More Likely to Die Than Whites

According to a study published July 7 on the Journal of the National Cancer Institute (JNCI) Web site, the survival disparity between white and black patients with gender-related cancers may be due to genetic and biological factors, rather than only socioeconomic and cultural factors.

The study, led by Dr. Kathy Albain of Loyola University (Ill.), examined records of 19,457 cancer patients who were tested by the Southwest Oncology Group between 1974 and 2001, and found that blacks with breast cancer, prostate cancer and ovarian cancer were more likely to die than white patients even if they received the same care. The study did not find the same disparity in examining lung cancer, colon cancer, lymphoma, leukemia or myeloma.

Albain told WebMD that the study suggests “as yet unidentified biologic factors” may be responsible for the disparities. “We don’t know what it is, but we know in our study the difference (in mortality) wasn’t related to access to care,” she said. “How could it be access when the access was the same?”

But Dr. Otis W. Brawley of the American Cancer Society, in an editorial for the JNCI, argues that, even though the patients received equal care after being diagnosed, social factors must still be considered.

“Some biological and even genetic differences in populations are not inherent from birth and immutable,” he writes. “They are influenced by environmental factors associated with [socioeconomic status] and culture. … It is unknown how poverty or wealth influences breast cancer pathology. It may be through differences in birthing habits, long-term diet, obesity, hormone use, or other factors.”

A second study published in the JNCI focused on the disparity in breast cancer. Previous research has suggested that black women are more likely to develop estrogen receptor-negative breast cancers, which are more difficult to treat. However, according to the JNCI study, this does not account for the disparity in mortality rates.

Lead researcher Idan Menashe of the U.S. National Cancer Institute said black women were more likely to die soon after diagnoses than white women, suggesting that socioeconomic factors are the cause of the disparity. “We think it's mostly access to care [with black women having less access], but we cannot rule out that the biological differences also contribute to the disparity,” he said.

Background: Diseases associated with population groups

There are several genetic diseases that are identified closely to one racial or ethnic group. For example, sickle cell disease, an inherited blood disorder, is especially prevalent in those of African, Caribbean or Middle Eastern descent. Tay-Sachs disease primarily affects Ashkenazi Jews, French-Canadian and Cajun populations. Ashkenazi Jews are also more likely to develop Crohn’s disease.

Researchers have been studying the human genome to identify genetic mutations that cause disease. A Long Island lab recently revealed that it is using the logic of the brainteaser Sudoku to determine the sequences of tens of thousands of DNA samples at a time. This technology may assist researchers in evaluating whole populations and determining whose genes point to future disease.

But doctors are cautious in treating patients differently according to race because, as Elijah Saunders, professor of Medicine at the University of Maryland School of Medicine, told Nature, it “could be useful but also dangerous when attributing health aspects to race and genetics ‘when we just don't know.’”

Nature also cites Joseph Graves Jr., professor of Evolutionary Biology at the University of Arizona, pointed out that “85% of all genetic variation occurs at the individual level” and asserted that the “complex interaction between socioeconomic and environmental conditions contributed more than genetics.”

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