In the United States, blacks have higher death rates from colon cancer than whites, and the survival disparity may be due in part to differences in screening programs and acute medical care in counties with a high concentration of blacks. We studied 148,947 Medicare beneficiaries with newly diagnosed colorectal cancer in 1989-1991 who resided in the 329 most populous counties in the United States to determine the relationship of race and county racial composition to cancer incidence and survival. Counties were divided into quartiles based on proportion of blacks in the population, and aggregate incidence and 2-year case-fatality rates were compared within and between quartiles. Within each quartile, the adjusted incidence rate for whites was consistently higher than that for blacks (P < 0.0001), and case-fatality rates were consistently lower among whites (P < 0.0001) for all but the quartile with the lowest proportion of blacks. Between quartiles, the incidence rates for both whites (P = 0.0001) and blacks (P = 0.008) decreased progressively, and case fatality rates increased progressively for both whites (P = 0.001) and blacks (P = 0.007) as the proportion of blacks increased. When counties were grouped into three different geographic areas, racial disparity in survival was observed in all regions. The variability between groups of counties in colon cancer incidence and mortality for both white and black patients may suggest differences at the county level in screening and treatment. However, consistent racial disparity within county quartiles may reflect persistent deficiencies in access to and quality of care for black patients.

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