Introduction:
Although overall incidence of colorectal cancer (CRC) is decreasing, an increasing incidence in younger individuals and distal/rectal cancer has been observed. Prior studies have also noted the association between lower socioeconomic status (SES) as well as race and higher CRC incidence rates. Given the variation of CRC incidence across age, race, and cancer site, we sought to evaluate the impact of SES on trends of CRC incidence across these demographics.

Methods:
Patients with a primary diagnosis of colorectal adenocarcinoma were identified in the SEER Research Plus Data (Specialized with Census Tract SES/Rurality) from 2006-2018. Cases were separated by race (non-Hispanic White (NHW), non-Hispanic Black (NWB), and Hispanic) and stratified by SES based on the Yost US-based index census tract. Further stratification was completed by age (<50 vs. ≥50) as well as by anatomic site (proximal vs. distal colon). Trends of CRC incidence were analyzed by joinpoint analysis by SEER*Stat and represented by annual percent change (APC) with significant difference from zero at α = 0.05.

Results
CRC incidence across all SES groups has decreased from 2006 to 2018 with the greatest decrease in individuals in the highest SES regions (APC: -3.5). When stratified by race, CRC incidence diverged between the highest and lowest SES among NHW and NHB but converged for Hispanics (Fig. 1). The divergence was particularly notable in NHB where the incidence ratio between highest and lowest SES decreased from 0.97 to 0.67. In younger patients, higher SES was also associated with a lower APC of distal tumors among NHW (1.8 for highest SES vs 2.93 for lowest SES). Additionally, a significant APC of 2.48 was noted in the young NHW population of the lowest SES group with proximal tumors. There was no significant APC in CRC incidence across all SES groups for both proximal and distal tumors in NHB individuals. Finally, in the young Hispanic population, only those in the lowest SES groups had a significant increase in APC (3.95 for lowest SES with distal tumors).

Discussion
In addition to observed racial and socioeconomic differences in CRC incidence trends over the past 13-year period, there appear to be interactions between race/ethnicity, age, and SES. Poverty rates impact the degree of CRC incidence change and reveal a widening disparity of CRC burden across SES. These data can help identify subgroups in particular need for chemoprevention and screening strategies.

David Hein

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