Incidence patterns of colorectal cancer in Norway 1993-2022 by age, site, and morphology.

Abstract

44 Background: The incidence of colorectal cancer (CRC) has decreased or stabilized in most high-income countries, but an alarming increase is observed in younger adults. Norway has high CRC incidence, which increased until the past two decades, then stabilized. A national screening program started in 2022; hence, this study is on a screening-naïve population. We aim to describe up-to-date incidence patterns of CRC, with emphasis on age-specific differences in tumor site and morphology. Methods: We extracted data on all CRC cases diagnosed 1993 to 2022 from the Cancer Registry of Norway, with completeness estimated to be >99%. Data was stratified by age groups (20-49, 50-74, and ≥75), sex, primary tumor location and morphology. Age-adjusted incidence rates were calculated using Stata 17 and analyzed using Joinpoint regression to provide annual percentage change (APC) and average annual percentage change (AAPC) of incidence rates. Results: There were 107 524 cases eligible for analysis. In the age group ≥75, overall incidence increased (AAPC 0.8), mainly caused by right-sided colon cancer (RCC), which increased until 2016 (APC 2.5), followed by a slight decrease (APC -0.9). The age group 50-74 had stable incidence (AAPC -0.2). Incidence in the age group 20-49 increased (AAPC 1.3), caused by left-sided colon cancer (LCC) and rectal cancer (RC). When stratifying on morphology, incidence of mucinous carcinomas was stable (AAPC -0.6), approx. 10% of all CRC cases. Neuroendocrine neoplasms (NEN) increased in all age groups (AAPC 4.2), accounting for only 1.4% of all CRC cases; but contributed somewhat to the overall incidence in age group 20-49, in particular RC where 8.8% of cases were NEN. In the age group 20-49, adenocarcinomas had an AAPC of 1.4, mucinous carcinomas -0.8, and NEN 4.1. Conclusions: We found an increasing incidence of CRC in the youngest (<50) and elderly (≥75). LCC and RC incidence increased in the youngest age group, still increasing up until 2022. In contrast, the increase in the elderly was mostly due to RCC. Different incidence patterns of primary tumor locations in younger and older age groups may imply differences in etiology and prognosis, different biological features and possibly therapeutic implications. [Table: see text]