Increasing Incidence of Colorectal Cancer in Young Adults.

Background: Colorectal cancer (CRC) incidence and mortality has been declining in the U.S. Despite success in reducing CRC incidence, incidence of early-onset CRC has increased markedly. In this study, we identified age-related disparities in CRC incidence and mortality, and investigated differences in anatomical distribution of colon cancers between populations.

Methods: CRC trends were evaluated using Surveillance, Epidemiology, and End Results Program Data from 1980-2016 for individuals under age 50 and 50 years and older. Rates and ratios were calculated using SEER^∗Stat. Regression analyses were calculated using Joinpoint.

Results: Increased CRC incidence among individuals under age 50 was observed. Among individuals under age 50, incidence-based mortality (IBM) stabilized, while incidence and IBM decreased for individuals aged 50 years and older. Normalized trends indicated increased rectal cancer incidence for individuals under age 50, particularly among individuals aged 30-39. Similar incidence of proximal and distal colon cancers in individuals under age 50 was observed, while colon cancers in individuals aged 50 and older were primarily distal.

Conclusions: We found age-related disparities in CRC incidence and IBM between individuals under age 50 and age 50 years and older. Increasing incidence rates of rectal cancer substantially accounts for this disparity among individuals under age 50. The escalating trends of early-onset CRC warrant investigation into the factors leading to the population-level trends.