A type of colon cancer that is linked to better outcomes occurs half as likely in Caucasian patients compared to African-Americans with colon cancer. The finding may provide insight into why African-Americans are more likely to die of colon cancer than Caucasians with the same stage of disease.
The population-based study of 503 people with colon cancer found that 14 percent of Caucasians and 7 percent of African-Americans had a genetic marker called microsatellite instability, or MSI. These types of tumors are known to be resistant to the chemotherapy drug 5FU. Yet, even without chemotherapy, these patients tend to have better outcomes.
"We know that patients with MSI colon cancer do better without chemotherapy. But these improved survival benefits are limited among African-Americans with colon cancer," says lead study author John M. Carethers, M.D., John G. Searle Professor and Chair of internal medicine at the University of Michigan Medical School.
The researchers identified patients through the North Carolina Colon Cancer Study, a population-based, case-control study conducted throughout central and eastern North Carolina. The North Carolina study includes both rural and urban areas, creating adequate representation by African-American and rural residents.
The group of patients Carethers and his colleagues looked at was 45 percent African-American and 55 percent Caucasian. Researchers examined tissue samples taken at the time of surgery and assessed it for various markers, including MSI.
In addition to the racial imbalance in MSI, the researchers also found that African-Americans patients were more likely than Caucasian patients to have cancer on the right side of their colon. This is significant because right-sided colon cancer is easier to miss with screening and more likely to be found larger or more advanced than left-sided cancers.
"Right-sided colon cancer may be the black ice of the colon - unseen but potentially deadly. Strategies to better recognize and detect right-sided cancer may need to be pursued in a broader fashion," Carethers says.
Additional authors: Bhavya Murali, Bing Yang, Ranor Basa, Mote Lee, Ryan Janke, Tina Ngo, Ruth Tejeda, Ming Ji, Matthew Kinseth, and Kathleen L. McGuire, from San Diego State University; Ryan T. Doctolero, Akihiro Tajima, E. Julieta Smith, Betty L. Cabrera, Katsumi Miyai, from University of California, San Diego; Temitope O. Keku, Christopher F. Martin, Joseph A. Galanko, Robert S. Sandler, from University of North Carolina, Chapel Hill
Funding: National Cancer Institute Comprehensive Partnerships to Reduce Cancer Health Disparities grants U54CA132384 and U54CA132379, and by National Institutes of Health grants R01 DK067287, U01 CA162147 and P30 DK034987
Reference: PLOS ONE, published June 23, 2014
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