Incidence trends and long-term survival in early-onset colorectal cancer: a nationwide Swedish study.

Background: Early-onset colorectal cancer (EOCRC, diagnosis before age 50) is increasing globally. Survival comparisons with late-onset colorectal cancer (CRC) are inconsistent, however, and long-term excess mortality remains poorly understood. This Swedish population-based study aimed to evaluate trends in incidence, survival, and long-term excess mortality in early- versus late-onset CRC.

Materials and methods: We identified all incident colorectal adenocarcinomas recorded in the Swedish National Cancer Register from 1993 to 2019. Incidence trends were quantified using annual percentage changes and relative survival differences were assessed using excess mortality rate ratios, both from Poisson regression models with 95% confidence intervals (CIs).

Results: A total of 47 864 right-sided colon, 40 664 left-sided colon, and 47 082 rectal cancer cases were included. EOCRC patients were more frequently diagnosed with metastatic disease, compared with late-onset CRC. EOCRC incidence increased across all subsites, with annual percentage changes ranging from 2.04 (95% CI 1.51-2.56) for rectal to 2.64 (95% CI 2.02-2.37) for right-sided colon cancer, while an increase among late-onset cases was observed only for right-sided colon cancer. Crude 5-year relative survival was similar across age groups, but after full adjustment (including metastatic stage), EOCRC was associated with better survival, with excess mortality rate ratios ranging from 0.76 (95% CI 0.68-0.84) for rectal cancer to 0.83 (95% CI 0.74-0.92) for right-sided colon cancer. Notably, excess mortality remained elevated 5-10 years after diagnosis in both age groups.

Conclusions: EOCRC incidence is increasing in Sweden, aligning with global trends. Although younger patients were more often diagnosed at an advanced stage of disease, they had similar crude survival and better stage-adjusted survival, compared with older patients. The persistent long-term excess mortality in both groups, even during periods when CRC patients are typically considered statistically cured, highlights the need for extended follow-up and tailored survivorship care.