Screening effectiveness and diagnostic gaps in early-onset colorectal cancer: A systematic review

The global incidence of early-onset colorectal cancer (EOCRC), defined as colorectal cancer diagnosed before 50 years of age, continues to increase despite advances in colorectal cancer (CRC) screening. Although several countries have lowered the recommended screening age to 45 years, uncertainty remains regarding whether current screening strategies adequately address the diagnostic burden of EOCRC. This systematic review synthesized the available evidence on population-based CRC screening, focusing on screening performance, detection gaps, and clinical outcomes in adults younger than 50 years. A systematic review was conducted using PubMed/MEDLINE, Scopus, and Web of Science to identify studies published between January 2000 and March 2026. Eligible studies evaluated screening performance, risk stratification, screening policy outcomes, or diagnostic delays in adults aged < 50 years. Methodological quality was assessed using study design-appropriate appraisal tools. Owing to substantial heterogeneity in study designs and outcome measures, findings were synthesized narratively according to the Synthesis Without Meta-analysis (SWiM) framework and organized into four pre-specified thematic categories. Forty-five studies met the inclusion criteria. Screening performance improved with increasing age, with adults aged 45-49 years demonstrating substantially higher detection rates of colorectal neoplasia and advanced adenomas than younger individuals. However, a considerable proportion of EOCRC cases occurred before 45 years of age and therefore remained outside current population-based screening eligibility. Across studies, younger adults also experienced more advanced disease at diagnosis and longer diagnostic intervals, highlighting persistent detection gaps despite recent reductions in the screening age. The current available evidence supports initiating average-risk CRC screening at 45 years but indicates that this strategy alone is insufficient to address the increasing burden of EOCRC. Future screening strategies should incorporate individualized risk assessment, earlier recognition of alarm symptoms, and timely diagnostic evaluation to improve early detection among adults younger than the current screening threshold.