Racial and Geographic Disparities in Colorectal Cancer Incidence and Associated County-Level Risk Factors in Mississippi, 2003-2020: An Ecological Study

Abstract

Introduction: Colorectal cancer (CRC) is the third most commonly diagnosed cancer in the United States (U.S.). Mississippi has the highest rate of CRC incidence in the U.S. and has large populations of black and white individuals, allowing for studies of racial disparities.

Methods: We conducted an ecological study using the county as the unit of analysis. CRC incidence data at the county level for black and white populations in Mississippi, covering the years 2003 to 2020, were retrieved from the Mississippi Cancer Registry. Age-adjusted incidence rate differences and their corresponding 95% confidence intervals (CIs) were then calculated for these groups. Getis-Ord Gi* hot and cold spot analysis of CRC incidence rate racial disparities was performed using ArcGIS Pro. We used global ordinary least square regression and geographically weighted regression (MGWR version 2.2) to identify factors associated with racial differences in CRC incidence rates.

Results: Age-adjusted CRC incidence rate in the black population (median = 58.12/100,000 population) and in the white population (median = 46.44/100,000 population) varied by geographical area. Statistically significant racial differences in CRC incidence rates were identified in 28 counties, all of which showed higher incidence rates among the black population compared to the white population. No hot spots were detected, indicating that there were no spatial clusters of areas with pronounced racial disparities. As a post hoc analysis, after considering multicollinearity and a directed acyclic graph, a parsimonious multiple regression model showed an association (β = 0.93, 95% CI: 0.25, 1.62) indicating that a 1% increase in food insecurity was associated with a 0.93/100,000 differential increase in the black-white CRC incidence rate. Geographically weighted regression did not reveal any local patterns in this association.

Conclusions: Black-white racial disparities in CRC incidence were found in 28 counties in Mississippi. The county-level percentage of food insecurity emerged as a possible predictor of the observed black-white racial disparities in CRC incidence rates. Individual-level studies are needed to clarify whether food insecurity is a driver of these disparities or a marker of systemic disadvantage in these counties.

Keywords: Mississippi; colorectal cancer; food insecurity; incidence; racial disparities.

Figure 1

Geographic distribution of potential predictors (percent smoking, percent obesity, percent uninsured, percent physical inactivity, median income, percent food insecurity, and percent diabetes mellitus) of county-level colorectal cancer incidence rate difference per 100,000, between black and white populations in Mississippi counties, 2003–2020.

Figure 2

Colorectal cancer incidence rates (2003–2020) among black and white populations by county. Data were obtained from the Mississippi Cancer Registry: (A) age-adjusted incidence rate (per 100,000) of colorectal cancer among the black population at the county level; (B) age-adjusted incidence rate (per 100,000) of colorectal cancer among the white population at the county level.

Figure 3

Colorectal cancer incidence rate differences per 100,000, between black and white populations in Mississippi counties, 2003–2020. Counties with significant rate differences (RDs) are indicated with a wider blue circle .