Understanding the burden of colorectal cancer in a three-county rural region of Michigan: an ecological analysis of incidence, mortality, and risk factors.

PURPOSE

Our aim was to identify whether known colorectal cancer (CRC) risk factors contribute to the high CRC burden in Michigan's Thumb region, a 3-county agricultural rural area in eastern Michigan.

METHODS

We examined county-level invasive CRC incidence and mortality rates (2000-2017) from the Michigan Cancer Surveillance Program and county-level data on CRC risk factors from publicly available datasets. Prevalence of CRC risk factors in the Thumb region were compared to Michigan's other rural and urban regions using ANOVA (Analysis of Variance) tests. Multivariable linear regression models with stepwise selection were used to assess whether living in the Thumb region was associated with increased CRC incidence, mortality, and late-stage diagnoses after accounting for other risk factors.

RESULTS

Living in the Thumb region (β = 10.4, p = 0.0003), obesity (β = 36.9, p = 0.04), and an unhealthy food environment (β = - 2.7, p = 0.003) were associated with higher CRC incidence. Smoking (β = 67.3, p < 0.0001), being uninsured (β = - 29.9%, p = 0.03), living in the Thumb region (β = 2.47, p = 0.03), lower colonoscopy screening (β = - 0.14, p = 0.01), and older age (β = 0.11, p = 0.006) were associated with higher CRC mortality. The percent of late-staged CRC diagnoses was significantly lower in the Thumb region than other rural and urban areas of the state (52.9%, 58.3%, and 54.6%, respectively, p = 0.03).

CONCLUSION

Findings suggest that living in Michigan's Thumb region is associated with higher CRC incidence and mortality compared to Michigan's other rural and urban regions, even after controlling for known risk factors. More studies on individual-level demographic, environmental, tumor, and treatment characteristics (e.g., treatment differences, water quality, pesticide use) are needed to further characterize these findings.