Early-onset colorectal cancer incidence in Norway: a national registry-based study (1993-2022) analyzing subsite and morphology trends.

Background: The overall incidence of colorectal cancer (CRC) has decreased or stabilized in most high-income countries, but an increase is observed in adults <50 years of age, termed early-onset colorectal cancer (EOCRC). Materials and methods: We conducted a nationwide registry-based study to provide up-to-date incidence patterns of EOCRC, with an emphasis on age-specific differences in tumor site and morphology. We extracted data from the Cancer Registry of Norway, with completeness estimated to be >99%. We calculated age-standardized incidence rates and used joinpoint regression to provide annual percentage change (APC) and average annual percentage change (AAPC). National screening started in Norway in 2022; hence, this study is on a largely screening-naive population. Results: There were 107 523 cases of CRC diagnosed between 1993 and 2022 eligible for analysis. The incidence of EOCRC (20-49 years) increased by 66% (AAPC 1.3), caused by left-sided colon and rectal cancers. The age group 50-74 years had a stable overall incidence (AAPC -0.2). In the age group ≥75 years, an increased incidence (AAPC 0.8) was observed, mainly by right-sided colon cancer, which increased until 2016 (APC 2.5), followed by a decrease (APC -0.9). EOCRC adenocarcinomas increased by 77% (AAPC 1.4). Neuroendocrine neoplasms were rare (1.4%), but increased in all age groups (AAPC 4.2). EOCRC showed a significantly higher proportion of distant metastases at time of diagnosis compared with the age group ≥75 years (28.6% versus 18.2%, Conclusions: We observed a sustained increase in EOCRC, caused by left-sided colon and rectal cancers. Unlike countries with established screening programs, the incidence of the age group >50 years remained stable or increased, but declined in recent years.