Population-based study of trends in early-onset cancer incidence rates in the Nordic countries, 2003-2022

Increasing incidence rates of early-onset cancer at ages 20-49 years have been reported in several countries, especially for colorectal, kidney, and breast cancer. A population-based study unsing the NORDCAN database investigated recent incidence trends of early-onset cancer in seven Nordic countries (Denmark, Faroe Islands, Finland, Greenland, Iceland, Norway, and Sweden) across 18 major cancer sites and compared to trends at ages 50-84 years. Age-standardized incidence rates (ASRs) per 100,000 person-years were calculated and linear regression applied to the log of ASRs to quantify the estimated annual percent change (EAPC) during 2003-2022. Early-onset cancer ASRs increased significantly for 12 of 18 evaluated cancer sites. The largest increases were observed for colon, kidney, and thyroid cancer (EAPCs > 2%), with the highest EAPC observed for colon cancer at < 35 years. Increases were also observed for melanoma, multiple myeloma, rectal, prostate, and liver cancer (EAPCs 1-2%). For thyroid cancer, the increases were similar among individuals aged 20-40 and 50-85 years, while for colon and kidney cancer the increases were higher among individuals aged 20-49 years. In contrast, the increases in melanoma and liver cancer were greater among those aged above 50 years. For cancer of the rectum, prostate, corpus uteri, and cervix uteri, the increases in early-onset incidence rates were contrasted by decreasing trends among older individuals. The relative increases translated into 9174 additional early-onset cases from 2003-2007 (n=47,491) to 2018-2022 (n=56,665). The authors conclude that the study showed increasing incidence rates of early-onset cancer across 12 major cancer sites in the Nordic countries. Explanations are likely multifold and cancer-specific, including changes in early-in-life risk factor exposures and increased diagnostic intensity, in particular for thyroid cancer.