Colorectal tumor patterns among adolescents, emerging adults, and young adults.
567 Background: Despite overall reductions in colorectal cancer (CRC) incidence, this trend has shifted among young individuals. Incidence rates continue to rise in this population, yet causes remain unknown. We examined CRC tumor patterns within the adolescent, emerging adult, and young adult (AYA) population in the United States. Methods: Using Surveillance, Epidemiology, and End Results program data, we identified individuals aged 15 to 39 years diagnosed with CRC from 2010-2014. Unadjusted and adjusted multinomial logistic regression models were used to quantify the associations between age of onset [adolescents (15-18 years), emerging adults (19-25 years) and young adults (26-29, 30-34, 35-39 years)] and CRC tumor site and sidedness. Results: We identified 4,417 AYA patients (33 adolescents; 298 emerging adults; 4,086 young adults) with CRC over the 5-year study period. The percentage of cases diagnosed with colon cancer decreased across all AYA groups compared to rectal cancer cases ( P-trend=0.03). Age group was associated with sidedness ( P-trend=0.01). Individuals aged 26 to 29 years remained more likely to be diagnosed with right-sided (Odds ratio, OR=1.35, 95% CI 1.08-1.69, P=0.009) and high-grade (OR=1.29, 95% CI 1.02-1.64, P=0.03) colorectal tumors compared to counterparts aged 35 to 39 years, after adjusting for sex, race/ethnicity, stage, grade, and county-level poverty. Conclusions: CRC site and sidedness were associated with age at diagnosis within the AYA population. These data are the first to define clinical patterns of CRC among AYAs. Elucidating etiologies underlying these patterns in young-onset CRCs are needed for tailoring CRC screening/surveillance and treatment.