Background
Accumulating evidence indicates that colorectal cancer (CRC) incidence is increasing among young adults, a pattern observed in several high-income countries. This rise contrasts with stable or declining rates in older age groups and remains poorly understood. Identifying whether these trends are consistent across countries, sexes, and age ranges may provide important clues regarding underlying causes.
Objectives
To characterise and compare temporal trends in colorectal cancer incidence among young people across multiple countries, examining differences by age group and sex, and identifying periods of acceleration in incidence rates.
Methods
We extracted age-specific colorectal cancer incidence rates from the IARC database for Norway, the United Kingdom, Sweden, Israel, the United States, and Canada. Analyses focused primarily on young adults aged 20–49 years, with additional analyses in narrower age groups (20–39 and 20–29 years) where data were available. Sex-specific trends were examined separately. Temporal trends were assessed using Joinpoint regression models, allowing for changes in slope over time. Annual Percentage Changes (APCs) and Average Annual Percentage Changes (AAPCs) were estimated, with model selection based on information criteria.
Results
Across most countries studied, colorectal cancer incidence increased among young adults, particularly in the 20–49-year age group. However, the timing, magnitude, and shape of trends varied substantially between countries and between the sexes. In several countries, relatively modest or flat trends in the late 1990s and early 2000s were followed by steeper increases from the mid-2000s or early 2010s onward. In others, increases were more gradual but sustained over the entire study period.
When examining younger age groups aged 20–39 and 20–29 years, increases were also evident and, in some, steeper than those observed in the 20–49-year group. For example, in Sweden, CRC incidence among individuals aged 20–29 years increased steadily from the mid-1990s through 2022, with no clear joinpoint detected, suggesting a persistent long-term rise. These findings indicate that the increase in early-onset CRC is not confined to those approaching screening age but is also present at much younger ages.
Conclusions
Colorectal cancer incidence among young adults is rising across multiple countries, though with marked heterogeneity in timing and magnitude by country, sex, and age group. The presence of increasing trends among individuals aged 20–29 years suggests that early-life or young-adulthood exposures may play an important role. Potential contributing factors include changes in diet (including increased consumption of red and processed meats and ultra-processed foods), rising prevalence of obesity and metabolic dysfunction, reduced physical activity, and broader environmental exposures. Differences in diagnostic practices are unlikely to fully explain the observed patterns. Further analyses are warranted to better understand these trends, including age–period–cohort modelling, examination of birth cohort effects, and integration of incidence trends with data on risk factor prevalence. By identifying populations, birth cohorts, and time periods at highest risk, this work can inform targeted prevention strategies, guide early-life and young-adulthood interventions, and support evidence-based decisions on risk-adapted screening and public health policies aimed at reducing the future burden of colorectal cancer.