Impact of Time Period and Birth Cohort on the Trend of Advanced Neoplasm Prevalence in the 40-49 Average-Risk Screening Population.

Background and aims: Early-onset colorectal cancer (CRC) is increasing globally. While the United States have lowered the age of initiation of screening to 45 years, other countries still start screening at 50 years of age. In Taiwan, the incidence of CRC has declined in 55- to 74-year-olds after the initiation of screening, but still increased in those 50-54 years of age, potentially due to rising precancerous lesion incidence in 40- to 49-year-olds. This study aimed to explore the chronological trend of the prevalence of colorectal advanced neoplasms (AN) in the screening population 40-54 years of age.

Methods: We retrospectively analyzed a screening colonoscopy cohort for prevalence of AN in average-risk subjects 40-54 years of age from 2003 to 2019. Logistic regression was used to distinguish cohort effect from time-period effect on the prevalence of AN.

Results: In total, 27,805 subjects (52.1% male) men were enrolled. There were notable increases in prevalence of AN in all 3 age groups during the 17-year span, but these were more rapid in those 40-44 years of age (0.99% to 3.22%) and 45-49 years of age (2.50% to 4.19%). Those 50-54 years of age had a higher risk of AN (adjusted odds ratio [aOR], 1.62; 95% confidence interval [CI], 1.19-2.19) in 2003-2008 but not in later periods (2009-2014: aOR, 1.08; 95% CI, 0.83-1.41; 2015-2019: aOR, 0.76; 95% CI, 0.56-1.03) when compared with those 45-49 years of age.

Conclusion: The prevalence of AN in those 40-54 years of age increased in the Taiwanese population, with a later birth cohort having a higher prevalence of AN. However, the prevalence of AN in those 45-49 years of age increased more remarkably and approximated that in those 50-54 years of age, which may justify earlier initiation of CRC screening in those 45 years of age.