ANN ARBOR, Mich. — African-Americans with colon cancer are half as likely as Caucasian patients to have a type of colon cancer that is linked to better outcomes. 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 5-fluorouracil, or 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,” said the study’s lead author, John M. Carethers, the John G. Searle Professor and Chair of Internal Medicine at the University of Michigan Medical School.
Results of the U-M study appear in the journal PLoS ONE.
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-American 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.
“Right-sided colon cancer may be the ‘black ice’ of the colon — unseen but potentially deadly.” Carethers says.
Carethers’ collaborators on the study are at San Diego State University; the University of California, San Diego; and the University of North Carolina at Chapel Hill.
National Cancer Institute Comprehensive Partnerships to Reduce Cancer Health Disparities and National Institutes of Health grants funded the research.