Background: Evidence indicates an increasing incidence of colorectal cancer (CRC) among individuals younger than 50 years, termed early-onset colorectal cancer (eoCRC).  Given that CRC represents a major public health burden in Poland, both in terms of incidence and mortality, understanding national eoCRC trends and absolute risk is essential to inform changes in evidence-based health system planning and screening programs that currently rely on endoscopy-based strategies.

Objectives: To describe trends in eoCRC incidence in Poland from 1999 to 2023 using population-based cancer registry data by sex and birth cohort, as previous estimates for Poland were geographically limited.

Methods: Incidence data for colorectal cancer (ICD 10 codes C18.0, C18.2-18.9, C19 & C20) diagnosed in Poland between 1999 and 2023 were obtained from the Polish National Cancer Registry, a nationwide population-based registry with mandatory reporting and full population coverage. We used population data from the National Central Statistical Office to calculate CRC incidence rates by sex and age group, including individuals aged 20–29 and 30–39 years, and five-year age groups among adults aged 40–74 years. Age standardization was performed using the Segi World Standard Population. Early-onset colorectal cancer (eoCRC) was defined as a diagnosis occurring between ages 20 and 49 years. Age-standardized incidence rates (ASIRs) were estimated for the period 2019–2023. Temporal trends were assessed by estimating average annual percent change (AAPC) for overall, age-specific, and early-onset incidence rates using Joinpoint regression models for 1999–2023. Age–period–cohort models were fitted to assess period and birth cohort effects.

Results:  A total of 405,160 CRC cases were identified. The overall ASIR was 22.5 (95% CI: 22.4–22.7) per 100,000 population, for men 29.1 (95% CI: 28.8–29.4) and women 17.7 (95% CI: 17.5–17.9) per 100,000 population. Overall CRC incidence increased (AAPC = 2.3%; 95% CI: 2.1–2.6), with steeper increases in men (AAPC = 2.6%; 95% CI: 2.4–2.9) than in women (AAPC = 1.8%; 95% CI: 1.6–2.1). Trends in eoCRC incidence also increased (AAPC = 1.3%; 95% CI: 1.0–1.7), including men (AAPC = 1.7%; 95% CI: 1.2–2.1) and women (AAPC = 0.7%; 95% CI: 0.7–1.8). Age–period–cohort models followed a J-shaped pattern, with lower risks among older cohorts and a sharp increase among those born after the 1970s. Men born in 1999 were 2.2 times more likely to develop colorectal cancer (95% CI: 1.3–3.8) compared with those born in 1949, whereas women born in 1999 had a 2.3-fold higher risk (95% CI: 1.2–4.5)
 
Conclusions: Population-based cancer registry data provide robust insight into eoCRC trends in Poland. Although eoCRC incidence remains lower, it is steadily increasing among younger adults. Individuals born after the 1970s had a higher CRC risk than those born in 1949, potentially reflecting the influence of major historical and societal transitions. Strengthening early detection through endoscopy-based strategies and implementing scalable, population-based screening with fecal immunochemical tests may help address this emerging burden.

Birth cohort-specific CRC incidence rate ratios in Poland, 1999-2023