Colon Cancer Race Gap May Be Explained by Underlying Health

Beth Skwarecki

December 16, 2014

The gap between black and white colon cancer patients' survival rates may be more a result of their health at diagnosis than differences in treatments, according to a matched cohort study published in the December 16 issue of the Annals of Internal Medicine.

"Our study suggests that the most effective route to reducing the racial survival disparity is to find ways to reduce the disparity in presentation, so fewer black patients present with advanced disease," Jeffrey Silber, MD, PhD, from the Center for Outcomes Research at The Children's Hospital of Philadelphia in Pennsylvania, and colleagues write.

Studying differences in 5-year survival after diagnosis, the team identified a gap of just 0.6%, out of an overall 9.9% gap between black and white patients, resulting from treatment effects.

The patients were all older than 65 years and receiving Medicare and were diagnosed between 1991 and 2005. A group of 7677 black patients was matched to three overlapping groups of 7677 white patients: one matched for demographics including age, sex, and location; one matched for demographics plus health at presentation (including comorbid conditions and tumor grade and stage); and one matched for demographics, presentation, and treatment.

The overall difference in 5-year survival between black and white patients was 9.9% (95% confidence interval [CI], 8.3% - 11.4%; P < .001), or a median survival time of 19 months. When black patients were matched with white patients with the same presentation of disease, the disparity fell to 4.9% (95% CI, 3.6% - 6.1%; P < 0.001). That number only changed slightly when the black patients were matched with white patients with the same demographics, presentation, and treatment (4.3%; 95% CI, 2.9% - 5.5%; P < .001).

That means treatment only made a difference of 0.6%, the authors write, with presentation characteristics accounting for most of the difference in the overall gap. After matching for demographics, presentation, and treatment, the authors explain that "[t]he residual disparity in the treatment match is similar to the 5-year survival disparity between black and white patients in the U.S. population as a whole. Although similar, we do not suggest that this is acceptable."

The team did not find significant differences between black and white patients in the rate of subsequent chemotherapy after the first year of treatment or in the quality of hospitals at which they were treated. They did find that the hazard ratio for similarly treated black and white patients became insignificant when adjusted for neighborhood median income (1.04; 95% CI, 0.98 - 1.11; P = .167) or for other measures reflecting poverty.

One coauthor reports receiving personal fees from Novartis and Genomic Health outside the submitted work. The other authors have disclosed no relevant financial relationships.

Ann Intern Med. 2014;161:845-854. Abstract

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