Where Can Colorectal Cancer Screening Interventions Have the Most Impact?

Discussion

In contrast with the large decline in colorectal cancer death rates experienced by most of the nation, our study identified three distinct areas in Appalachia and the rural South where progress has lagged. These findings expand on previously reported state disparities in colorectal cancer death rates (3) and are consistent with recent research linking rural residence with increased risk of colorectal cancer death (12, 13). The trends in Hotspots 1 and 3 are also compatible with the historical shift in the burden of colorectal cancer from more to less affluent individuals (5). The patterns in colorectal cancer death rates in these high-risk areas are more similar to those in economically transitioning countries with limited health care resources, such as Romania, Russia, and Mexico (14), than to those in the United States.

The Lower Mississippi Delta and Appalachia are diverse geographic regions distinguished by longstanding challenges that include high unemployment, low levels of education and health literacy, and inadequate access to health care (15–18). The Lower Mississippi Delta has been classified as persistently poor (≥20% poverty) since 1970 by the U.S. Department of Agriculture's Economic Research Service and has county-level poverty rates that are two standard deviations above the national median (19, 20). High poverty similarly characterizes much of Appalachia and rural North Carolina and Virginia (21). In Appalachia, Central Appalachia is the most poverty-stricken subregion, where ≥20% of people live in poverty in most counties (22). Individuals who are economically disadvantaged have higher colorectal cancer death rates due to both higher incidence rates and poorer disease outcomes. Survival rates among low-income individuals are lower due to a variety of factors, including a higher prevalence of comorbidities, a lower likelihood of tumor resection and adjuvant therapy, and more advanced disease stage (12, 23, 24). Later stage at diagnosis is largely a consequence of lower screening rates among people with lower socioeconomic status (25, 26), often as a result of obstacles in accessing health care. Notably, as of March 2015, only six of the 12 states found to contain high-risk counties have taken advantage of the federal funding opportunity offered by the Affordable Care Act to expand Medicaid coverage (Arkansas, Illinois, Indiana, Kentucky, Ohio, and West Virginia).

Research has demonstrated the efficacy of screening for reducing colorectal cancer mortality both by decreasing incidence through the removal of precancerous lesions and by detecting malignancy at an earlier, more treatable stage (27). Colorectal cancer screening rates have been increasing in the United States since at least 1987 (25, 28), but uptake has not been equally distributed and disparities by race, ethnicity, and socioeconomic status remain (25, 29). For example, in 2010, 40% of individuals with incomes less than 200% of the federal poverty threshold were current for colorectal cancer screening, compared with 66% of those with incomes of more than 500% of the poverty threshold (30). Area-level poverty is associated with screening behavior independent of individual factors; people who reside in communities with high poverty are less likely to be screened than those living in low-poverty settings even after controlling for income, education, and insurance status (31). The rural poor are at a particular disadvantage because of the low density of specialists for colorectal cancer screening and treatment (32, 33). Disparities by insurance status are even more striking. In 2010, just 19% of individuals without health insurance were current for colorectal cancer screening compared with 62% of those with coverage (34). The Delta Rural Poll found that 22% of Mississippi Delta residents were uninsured in 2009 (35), compared with 17% in the general U.S. population (36). In west central Appalachia, the uninsured rate is more than 19% in the majority of counties, and as high as ≥25% in many counties (22).

Screening inequalities likely contribute to the disparities we observed. Screening in accordance with guidelines has been estimated at 49% in Appalachian Ohio (37), which has among the lowest rates of uninsured in Appalachia (22). Fleming and colleagues found that among Kentucky residents, those living in Appalachia were half as likely as non-Appalachians to report endoscopy screening for colorectal cancer in the past 10 years (38). While colorectal cancer screening rates for the Mississippi Delta are not available, breast cancer screening has been shown to be lower there than in the rest of the United States (39). In addition, a study of cancer incidence in Mississippi found that rural residence was associated with a later stage of disease, which is suggestive of lower screening prevalence in the predominantly rural Delta region (40). According to Behavioral Risk Factor Surveillance System data for 2010, colorectal cancer screening rates were below the national median (64.5%) in each of the 10 states represented in Hotspots 1 and 2, with West Virginia (54.5%), Mississippi (57.1%), and Arkansas (58.6%) ranking in the lowest quartile (41). It is noteworthy that none of the 12 states with counties identified as high-risk in our analysis are among the 25 states funded by the Centers for Disease Control and Prevention's Colorectal Cancer Control Program, which provides screening services to uninsured and underinsured low-income individuals.

Screening disparities primarily relate to cost and access to care. Income and education are strongly, positively associated with screening, even among insured individuals with a usual physician (42). Other factors associated with low screening rates include lack of knowledge about the importance of screening (43), not having a usual place for health care, and not having a physician recommendation for the test (44). However, a large proportion of underserved patients do not follow through with testing even after a provider recommendation (45). A common provider barrier to screening in underserved communities is an inadequate referral mechanism after an abnormal test (46). Patient navigators or community health workers are particularly beneficial for facilitating follow-up and treatment in underserved populations (47).

Obesity (body mass index ≥ 30 kg/m²) increases the risk of colorectal cancer 2-fold in men and by 50% in women (48). With the exception of Virginia, all of the hotspot states are in the highest quartile for obesity prevalence among adults (49). Within Mississippi, which has the highest obesity prevalence of any state (35% vs. a national median of 27% in 2009), the highest county-level obesity rates (38% to 44%) are concentrated in the Mississippi Delta region (50). In addition, food consumption in the Delta, which is high in soft drinks, red meat, and salty snacks, differs from national patterns in a direction conducive to colorectal cancer development (51). Moreover, Mississippi and West Virginia residents are least likely to participate in leisure-time physical activity (67% vs. the U.S. median of 76%), which protects against colorectal cancer (52).

The primary strength of our study is the innovative use of advanced spatial analysis to analyze four decades of nationwide, county-level vital statistics data and pinpoint geographic disparities in colorectal cancer death rates. Although we were limited to the study of counties with a minimum of 10 deaths per decade in order to produce reliable rates, this represented 93% of all counties during 2000 to 2009 and the Spatial Weight Matrix accounted for these missing data. Due to the nature of ecologic studies, we can only speculate about causes for the disproportionate burden of colorectal cancer. We are also somewhat limited in the interpretation of our results. For example, some portion of the increase in the risk of colorectal cancer death in the Lower Mississippi Delta hotspot is likely due to the shift in the racial distribution of the population, from 32% black in the early 1970s to 37% during 2009 to 2011. However, the effect of population migration on our results was likely minimal because both blacks and whites had similarly elevated risk. The interpretation of death data is also limited by inaccuracies in the underlying cause of death recorded on death certificates. However, misclassification for colorectal cancer is only about 10% (53).

Although the risk of death from colorectal cancer is at a historical low for most Americans, it is unnecessarily high among residents of the Lower Mississippi Delta, Appalachia, and other rural areas. Cancer prevention through lifestyle modification is the preferable mechanism for decreasing cancer occurrence; however, effecting change to reduce obesity and increase physical activity is extremely difficult. Moreover, the fruits of these efforts are not born at the population level for many years. Promoting and improving access to screening through patient navigation and outreach programs offers a more immediate return on investment. The state of Delaware effectively eliminated colorectal cancer disparities in less than a decade by implementing comprehensive statewide colorectal cancer screening (54). The rapid introduction of coordinated, targeted, community-based screening programs in these high-risk areas could be similarly successful.