Abstract IA10: Colorectal cancer mortality along the U.S.-Mexico border
Authors: Murphy Caitlin C. 
Published: September 2020

Abstract
Colorectal cancer (CRC) incidence and mortality have changed strikingly in the U.S. over the past three decades. Incidence and mortality rates have decreased among older adults since the early 1990s, largely due to improvements in average-risk screening. By contrast, incidence rates have rapidly increased in younger (age &lt;50 years) adults, but little is known about the mechanisms contributing to young-onset CRC. These changes in incidence and mortality rates have not occurred equally by race/ethnicity or geography. To better understand the burden of CRC among Hispanics, we examined CRC mortality along the U.S.-Mexico border. We used data from the National Center for Health Statistics to estimate age-adjusted (to the 2000 U.S. standard population) mortality rates per 100,000 persons. We compared mortality rates between counties on the U.S.-Mexico border (41 counties in California, Arizona, New Mexico, and Texas) to non-border counties in the same states, overall and by ethnicity (Hispanic vs. non-Hispanic white) and age (+/- 50 years). From 1990 to 2016, there were 25,057 CRC deaths in counties along the U.S.-Mexico border and 1,453,410 deaths in non-border counties. Age-adjusted mortality rate was 21.1 per 100,000 and 25.9 per 100,000 in border and non-border counties, respectively (rate ratio [RR] 1.23; 95% CI 1.21, 1.24). Rates decreased over time in both border and non-border counties: from 26.9 per 100,000 to 17.8 per 100,000 in border counties and from 33.9 per 100,000 to 19.9 per 100,000 in non-border counties. There were differences in mortality by county and ethnicity in older adults (age ≥50 years). Specifically, the lowest overall mortality rate was among Hispanics living in border counties (43.1 per 100,000), and the highest was among whites in non-border counties (58.6 per 100,000). These differences disappeared over time, and in 2012-16, mortality rates across the four subgroups were similar (border: 42.3 per 100,000 non-Hispanic whites, 41.6 per 100,000 Hispanics; non-border: 44.8 per 100,000 non-Hispanic whites, 41.8 per 100,000 Hispanics). Mortality rates in younger adults increased from 1990 to 2016, and rates were slightly higher in non-border counties. For example, in 2012-16, age-adjusted mortality of young-onset CRC was 2.6 per 100,000 in border counties compared to 2.9 per 100,000 in non-border counties (RR 1.11; 95% CI 1.00, 1.23). We observed lower CRC mortality rates in counties along the U.S.-Mexico border, particularly for older Hispanics. The mortality advantage in this subgroup declined over time, driven by improvements in non-border counties and among non-Hispanic whites. Rates remained stable among Hispanics in border and non-border counties. Younger adults experienced CRC-related mortality, regardless of county or ethnicity. These findings may reflect generational or birth cohort differences in cancer risk.
Citation Format: Caitlin C. Murphy. Colorectal cancer mortality along the U.S.-Mexico border [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr IA10.