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Higher colon cancer mortality in African-Americans linked to microsatellite instability
Colon cancers in African-American patients showed half the prevalence of microsatellite instability compared with Caucasians, without an increase in CD8+ T-cell infiltration, and may contribute to their higher mortality rates, according to research data.
As part of the North Carolina Colon Cancer Study, John M. Carethers, MD, division of gastroenterology, department of internal medicine, University of Michigan Health System, and colleagues conducted a population-based case-control investigation of colon cancer (CC) patients identified between October 1996 and September 2000. Random samples were selected to ensure an equal number of African-Americans and Caucasians, resulting in 503 CC cases (45% African-American) and 1,048 controls (42% African-American).
The researchers sourced epidemiological data from the state cancer registry, and independent DNA analysis was done on each patient’s colorectal tumor and surrounding tissue for microsatellite instability (MSI). Immunohistochemistry for CD8+ T-cell count analysis also was performed.
Overall MSI was observed in 11% of CC cases, with 14% MSI among Caucasians compared with 7% in the African-American group (P=.009). MSI cancers were clinically similar between races, but among microsatellite stable (MSS) cancers, African-American patients were younger (62.6 vs. 64.8 years; P=.02), more likely to be women (56% vs. 43%; P=.008), and more likely to have proximal tumors (54% vs. 44%; P=.04). Average CD8+ T-cell counts were higher in MSI cancers compared with MSS (88 per high power field vs. 30.4 per high power field; P<.0001). While overall counts were not significantly different between races, the mean CD8+ T-cell count was consistently lower in African-Americans than in Caucasians who more often had high infiltrations.
"Our study shows that a good prognostic marker for outcome from colon cancer, MSI, is half as prevalent in African American patients compared to Caucasian patients," Carethers told Healio.com/Gastroenterology. "This does not appear to be due directly to the level of inflammation that is associated with the MSI marker, so the full rationale for the difference is not apparent. However, the reduction of MSI prevalence in the African American CC population likely contributes to the overall poor survival in this group compared to Caucasians."
Disclosure: The researchers report no relevant financial disclosures.