OBJECTIVES: The incidence of colorectal cancer (CRC) has declined in recent years for people of all races/ethnicities; however, the incidence of invasive CRC is increasing in younger adults. Our primary objective was to compare age-adjusted incidence of early- and late-onset CRC among SC residents to overall US estimates.

METHODS: Incident cases of CRC from January 1, 2001 through December 31, 2015 were retrieved from the National Program of Cancer Registries and NCI’s Surveillance, Epidemiology, and End Results (SEER) program using SEER*Stat. Incidence rates were calculated as five-year moving averages based upon age at CRC onset (early, 0-49 years; late, 50+ years) among SC and the entire US population. Subgroup analyses by sex/race classification were performed. Rates were expressed per 100,000 and age-adjusted to the 2000 US census standard population (19 age groups). A rate ratio (RR) and corresponding p-value were calculated for comparisons between SC and US. A 95% confidence interval was calculated for rates and ratios according to the methodology developed by Tiwari.

RESULTS: A total of 2,160,038 malignant CRC cases were recorded in the US, including 32,585 cases in SC. A consistent trend of increased EOCRC incidence was observed in SC, 8.2 vs. 6.4 (RR_2001-2015 1.28; 95% CI 1.21-1.36) and 8.1 vs. 7.4 (RR_2011-2015 1.10; 95% CI 1.04-1.16). In the subgroup analysis, EOCRC incidence was significantly increased among all Whites, White males, and all males in SC during 2011-2015. Conversely, late-onset CRC has declined in both SC, from 171.6 to 114.6, and the US, from 170.3 to 120.4, during the study period. However, we observed a trend towards lower incidence in SC since 2004-2008 (RR_2011-2015 0.95; 95% CI 0.93-0.97).

CONCLUSIONS: Contrasting incidence rates were observed between the US and SC for both early- and late-onset CRC. This variance may represent differences in populations, screening, or risk factor exposure.