Colorectal Cancer and Precursor Lesion Prevalence in Adults Younger Than 50 Years Without Symptoms.

Importance: Incidence of colorectal cancer (CRC) is increasing among younger adults. However, data on precursor lesions in patients who are asymptomatic, especially those aged younger than 50 years, are lacking. Objective: To analyze the prevalence and number needed to screen (NNS) for adenomas, advanced adenomas, and serrated lesions, as well as the incidence of CRC in patients older than age 20 years. Design, Setting, and Participants: This cohort study was conducted among 296 170 patients who received a screening colonoscopy within a national screening colonoscopy registry from 2012 to 2018 in Austria, including 11 103 patients aged younger than 50 years. CRC incidence was analyzed using data from Statistic Austria from 1988 to 2018. Data were analyzed in September 2021. Main Outcome and Measures: The prevalence of adenomas and other lesions and the incidence of CRC in individuals aged 20 years or older were assessed. Results: Among 296 170 patients included in the study (median [IQR] age, 60 [54-68] years; 150 813 females [50.9%]), 11 103 patients (3.7%) were aged younger than 50 years and 285 067 patients (96.3%) were aged 50 years or older. Among patients younger than age 50 years, 1166 individuals (10.5%; NNS = 9) had adenomas and 389 individuals (3.9%; NNS = 26) had at least 1 advanced adenoma, while among those aged 50 years or older, 62 384 individuals (21.9%; NNS = 5) had adenomas and 19 680 individuals (6.9%; NNS = 15) had at least 1 advanced adenoma. Among 1128 males aged 40 to 44 years, 160 individuals (14.2%; NNS = 7) had at least 1 adenoma, and among 1398 females aged 40 to 44 years, 114 individuals (8.1%; NNS = 12) had at least 1 adenoma. The prevalence of adenomas for individuals aged 45 to 49 years vs 50 to 54 years was 490 of 2879 males (17.1%; NNS = 6) vs 8269 of 40 935 males (20.2%; NNS = 5) and 284 of 2792 females (10.2%; NNS = 10) vs 4997 of 40 303 females (12.4%; NNS = 8), respectively. Prevalence of adenomas changed from 61 of 498 individuals (12.4%) in 2008 to 150 of 1064 individuals (14.1%) in 2018 among those younger than 50 years and from 2646 of 12 166 individuals (21.8%) to 10 673 of 37 922 individuals (28.2%) among those aged 50 years and older. The prevalence of advanced adenomas changed from 20 individuals (4.0%) in 2008 to 55 individuals (5.2%) in 2018 in individuals younger than 50 years and from 888 individuals (7.3%) in 2008 to 2578 individuals (6.8%) in 2018 among those aged 50 years and older. Among individuals younger than age 50 years, CRC incidence per 100 000 individuals changed from 9.1 incidents in 1988 to 10.2 incidents in 2018 among males (average annual percentage change [AAPC], 0.5%; 95% CI, 0.1% to 1.0%) and from 9.7 incidents in 1988 to 7.7 incidents in 2018 among females, with a nonsignificant AAPC (-0.2%; 95% CI, -0.7% to 0.3%). Among individuals aged 50 years or older, CRC incidence per 100 000 individuals changed from 168 incidents in 1988 to 97 incidents in 2018 among females (AAPC, -1.8%; 95% CI, -1.9% to -1.6%), and 217 incidents in 1988 to 143 incidents in 2018 among males (AAPC, -1.2%; 95% CI, -1.3% to -1.1%). Conclusion: In this study, CRC incidence decreased after 1988 in Austria among individuals older than 50 years, while among patients younger than 50 years, incidence increased among males but decreased among females. Prevalence of adenomas increased in all age groups, while advanced adenoma prevalence increased among patients younger than 50 years but decreased in patients aged 50 years and older.