Introduction

Colorectal cancer (CRC) incidence and mortality rates are increasing in adults aged <50 years. Young-onset adenoma (YOA)-adenoma detected in adults younger than 50 years-may signify increased CRC risk, but this association has not been widely studied. Our aim was to compare the risk of incident and fatal CRC in adults aged <50 years with YOA diagnosis compared with those with a normal colonoscopy.

Methods

We conducted a cohort study of US Veterans aged 18-49 years who received colonoscopy between 2005 and 2016. The primary exposure of interest was YOA. Primary outcomes included incident and fatal CRC. We used Kaplan-Meier curves to calculate cumulative incident and fatal CRC risk and Cox models to examine relative CRC risk.

Results

The study cohort included 54,284 Veterans aged <50 years exposed to colonoscopy, among whom 13% (n = 7,233) had YOA at start of follow-up. Cumulative 10-year CRC incidence was 0.11% (95% confidence interval [CI]: 0.00%-0.27%) after any adenoma diagnosis, 0.18% (95% CI: 0.02%-0.53%) after advanced YOA diagnosis, 0.10% (95% CI: 0.00%-0.28%) after nonadvanced adenoma diagnosis, and 0.06% (95% CI: 0.02%-0.09%) after normal colonoscopy. Veterans with advanced adenoma had 8-fold greater incident CRC risk than those with normal colonoscopy (hazard ratio: 8.0; 95% CI: 1.8-35.6). Across groups, no differences in fatal CRC risk were observed.

Discussion

Young-onset advanced adenoma diagnosis was associated with 8-fold increased incident CRC risk compared with normal colonoscopy. However, cumulative CRC incidence and mortality at 10 years among individuals with either young onset non-advanced or advanced adenoma diagnosis were both relatively low.