Colorectal tumor patterns among adolescents, emerging adults, and young adults.

567Background: 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). A...