A screening-threshold-oriented framework reveals threshold-adjacent redistribution of global colorectal cancer...

Conventional age <50 versus ≥50 years grouping may obscure colorectal cancer (CRC) burden patterns around the contemporary screening boundary. We examined whether adults aged 45-49 years occupy a threshold-adjacent position not captured by conventional grouping.

Using GBD 2023 data, we analyzed CRC incidence, deaths, and DALYs from 1990 to 2023 across four age groups (15-44, 45-49, 50-74, 75+ years). We assessed global and SDI-stratified trends, inequality, empirical lower-bound burden frontiers, and decomposition of burden change. Sensitivity analyses included conventional age regrouping, High versus Non-High SDI decomposition, split-period analyses, and adjacent 5-year age-group comparisons.

Incidence rose most in adults aged 15-44 (+16.8%) and 45-49 years (+11.0%), with smaller increases in those aged 50-74 (+7.5%) and 75+ (+3.6%). Deaths and DALYs declined more clearly above age 50. In adults aged 45-49, incidence inequality remained positive but narrowed (CI: 0.304 to 0.253; relative SII: 1.693 to 1.412), while DALY inequality weakened (CI: 0.159 to 0.068). During 2010-2023, the residual rate-change component contributed positively to incidence in adults aged 45-49 globally (31.5%) but was slightly negative in those aged 50-74 (-2.6%). Post-2018 amplification in High-SDI populations was consistent with screening-related detection effects.

Adults aged 45-49 occupy a context-dependent threshold-adjacent position in global CRC burden redistribution. These findings inform population-level surveillance and policy evaluation rather than individual-level clinical decision-making.