In colon cancers, the prevalence of microsatellite instability, a genetic biomarker of hypermutable colon cancers, is only half as high among African American patients as among white patients, according to a report published online June 24 in Public Library of Science One.
Microsatellite instability generally predicts a better outcome for patients, compared with same-staged colon cancers that don’t have it. This may be due to the generation of neoantigens and an associated attraction of immune cells that could limit tumor growth and metastasis. Thus, this discrepancy between African Americans and whites in the rate of microsatellite instability may contribute to the well-known racial disparity in mortality from the disease, said Dr. John M. Carethers of the University of Michigan, Ann Arbor.
To explore whether the rate of microsatellite instability in colon cancers differs by race, Dr. Carethers and his associates analyzed data from a population-based, case-control cohort that oversampled African Americans – the North Carolina Colon Cancer Study. They performed DNA extraction and microsatellite analysis on 503 stored samples of invasive adenocarcinomas from African American (45%) and white (55%) patients who had been diagnosed in 1996-2000. Overall, 11% of these tumors showed microsatellite instability.
The prevalence of microsatellite instability was 7% in tumors among black patients, compared with 14% in tumors among white patients (PLoS One 2014 June 24 [doi:10.1371/journal.pone.0100461]).
In this study, as in previous studies, most colon cancers that did not carry microsatellite instability were proximal. Accordingly, African American patients were more likely than were whites to have proximal rather than distal tumors. The reason for this difference in tumor location is not yet known, but the finding "has implications for the approach to colon cancer screening in this population," the researchers noted.
This study was funded in part by the National Cancer Institute. Dr. Carethers and his associates reported no financial conflicts of interest.
