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The underlying causes of this increase are not fully understood. The researchers note that the trend does not appear to be driven by known risk factors for colorectal cancer in younger people, such as inflammatory bowel disease and hereditary factors. Instead, environmental and lifestyle factors early in life may play a role.

"Childhood obesity, a sedentary lifestyle, and antibiotic use have been suggested as contributing factors, although the underlying biological mechanisms remain unclear, " says Cecilia Radkiewicz, researcher at the Department of Molecular Medicine and Surgery at Karolinska Institutet, who led the study.

"Incidence Trends and Long-Term Survival in Early-Onset Colorectal Cancer: A Nationwide Swedish Study" is published in Annals of Oncology.

Younger people more often have advanced disease

The study also found that younger patients are more likely to have advanced (metastasized) disease at diagnosis compared with older patients, suggesting that symptoms may have gone unnoticed for longer before the cancer was detected.

"Since the chances of cure increase with early detection, it is important that both the public and health care professionals are aware that colorectal cancer can also affect younger people. At the same time, younger patients are more likely to tolerate extensive surgery and treatment, which is reflected in our results showing a more favorable prognosis compared with older patients, " says Radkiewicz.

Another important finding is that mortality remains elevated in both younger and older patients for up to ten years after cancer diagnosis.

"This is remarkable, as patients are often considered cured after such a long time. Our results challenge this view and highlight the need for further research into the underlying causes, as well as long-term follow-up and support for both younger and older patients, " says Radkiewicz.

More information: Shabane Barot et al, Incidence Trends and Long-Term Survival in Early-Onset Colorectal Cancer: A Nationwide Swedish Study, Annals of Oncology (2025). DOI: 10.1016/j.annonc.2025.07.019  Journal information: Annals of Oncology