BACKGROUND AND AIMS: Incidence and mortality from early onset colorectal cancer (CRC) is rising. Adenoma detection, removal and subsequent endoscopic surveillance may modify risk of CRC diagnosed prior to age 50 (early onset CRC). We conducted a systematic review of young onset adenoma (YOA) prevalence, associated risk factors, and rate of metachronous advanced neoplasia after YOA diagnosis. METHODS:Through a systematic search of multiple electronic databases through 2/12/2019, we identified studies with individuals age 18 to 49 years which reported on prevalence of adenoma, risk factors for adenoma, and/or risk for metachronous advanced neoplasia. Summary estimates were derived using random effects meta-analysis, when feasible. RESULTS:Pooled overall prevalence of YOA was 9.0% (95% CI: 7.1%-11.4%) based on 24 studies including 23,142 individuals. On subgroup analysis, pooled prevalence of YOA for autopsy studies was 3.9% (95% CI: 1.9%-7.6%), while prevalence for colonoscopy studies was 10.7% (95% CI: 8.5%-13.5). Only advancing age was identified as a consistent risk factor for YOA based on 4 studies including 78,880 individuals. Pooled rate of metachronous advanced neoplasia after baseline YOA diagnosis was 6.0% (95% CI: 4.1%-8.6%), based on 3 studies including 1,493 individuals undergoing follow-up colonoscopy, with only 1 CRC case reported.Overall there were very few studies reporting metachronous advanced neoplasia, and no studies evaluating whether routine surveillance colonoscopy decreases risk of CRC. CONCLUSIONS:Prevalence of YOA is estimated to be 9% and increases with age. Risk for metachronous advanced neoplasia after YOA diagnosis is estimated to be 6%. More research is needed to understand the prevalence, risk factors, and risk of CRC associated with YOA.

Background Early onset colorectal cancer (CRC) incidence is rising under age 50, with a birth cohort effect for increasing incidence among individuals born 1950 and later. It is unclear whether increasing incidence trends will confer increased risk beyond age 50, the previously most commonly recommended age to initiate screening, when screening availability might modify incidence trends. Aim Evaluate US trends in colorectal cancer (CRC) for ages 40-59 years. Methods We analyzed counts and incidence rates for CRC, including by anatomic subsite, using the US Cancer Statistics dataset covering 100% of the population 2003-2017. Joinpoint regression was used to quantify Average Annual Percent Change (AAPC) in cancer incidence by age subgroup. Results 470,458 CRC cases were observed age 40-59, with absolute numbers of rectal (n = 4173) and distal cases (n = 3327) per year for age 50-54 approaching age 55-59 cases for rectal (n = 4566) and distal (n = 3682) cancer by 2017. Increasing early onset rectal cancer incidence per 100,000 occuring under age 50 was observed to extend to age 50-54, from 4.9 to 6.3 for age 40-44 (AAPC 2.1; 95% CI 1.5-2.7), 9.3 to 12.0 for age 45-49 (AAPC 1.5; 95% CI 1.1-1.4), and from 16.7 to 19.5 for age 50-54 (AAPC 1.0; 95% CI 0.7-1.3). Conclusions CRC trends suggest observed increased risks under age 50 are also present after age 50, despite prior availability of screening for this group. Recent CRC trends support initiation of screening earlier than age 50, and promotion of "on-time" screening initiation.