While most of the United States has experienced large declines in colorectal cancer death rates in recent years, progress in the Mississippi Delta and two other areas has lagged. The lower Mississippi Delta, encompassing 94 counties, was identified as the hot spot with the highest colorectal cancer death rates, followed by 107 counties in west central Appalachia, and 37 counties in eastern Virginia/North Carolina.
The study is published in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research
Siegel explained that over the past few decades we have learned how to prevent most colorectal cancer deaths, which has led to a drop in the U.S. colorectal cancer death rate by half. However, progress has not been equivalent in all states, and large differences exist among states, which she and her colleagues identified in a previous study. For this study, the researchers gathered and analyzed data at a more granular level because targeted interventions are often more feasible on a smaller scale, she said.
Siegel and colleagues used a geospatial software tool to identify areas of very low rates of colorectal cancer deaths, called cold spots, and areas of very high rates, called hot spots. For areas identified as hot spots, death rates were plotted from 1970 to 2011 and rate ratios were calculated to compare trends over time between hot spots and the rest of the United States.
Graphic Courtesy of the American Cancer Society
Using this spatial mapping, the researchers identified three distinct hot spots. The lower Mississippi Delta hot spot had colorectal cancer death rates that were 40 percent higher than the nonhot spot areas in the country during 2009-2011. Rates in the hot spots in west central Appalachia and eastern Virginia/North Carolina were 18 percent and 9 percent higher, respectively, than those of the nonhot spot areas in the country during this time period.
The colorectal cancer death rate increased steadily, by 3.5 percent per year, for black men in the lower Mississippi Delta between 1970 and 1990, and has since remained unchanged.
The authors also noted in their paper a crossover of death rates in the lower Mississippi Delta with those in the rest of the United States around 1990: In the early 1970s, death rates in the delta were 18 percent lower than the average death rates in the country.
In an interview, Siegel said, "We expanded on an earlier state-level analysis by using a geospatial software tool to identify clusters of counties in the United States that have unnecessarily high colorectal cancer death rates. We identified three distinct hot spots - the lower Mississippi Delta, west central Appalachia, and eastern Virginia/North Carolina - where colorectal cancer death rates are elevated compared with most of the country," Siegel added. "Further, while the rates have begun to decrease in the lower Mississippi Delta for most population groups, they remain stagnant in black men.
"These areas are low-hanging fruit for colorectal cancer screening interventions," Siegel said.
"Although we've made great strides against colorectal cancer in a fairly short time period, there are a lot of vulnerable populations that aren't benefiting. Now that these groups have been identified, there is a moral obligation to do something about it," Siegel said. "Targeted interventions, like using people within the community to talk to their neighbors about screening, are likely to be effective. We know interventions work because we have an example in Delaware, where they implemented statewide colorectal cancer screening and effectively eliminated disparities in less than a decade."