Early-onset colorectal cancer: what 40 years of data show

Swiss registry data covering 96,410 colorectal cancer cases from 1980 to 2021 show that incidence in adults under 50 has risen by about 0.5% a year, to nearly 7 cases per 100,000 person-years. Over the same period, rates fell in adults aged 50 to 74. The study, in the European Journal of Cancer in 2026, describes what is changing and admits what is not yet explained.

What did the Swiss study find about colorectal cancer in adults under 50?

Researchers at the University of Geneva and Geneva University Hospitals analysed cancer registry data from the Geneva Cancer Registry and Switzerland’s National Agency for Cancer Registration. According to the University of Geneva’s summary:

• Cases diagnosed before age 50 made up 6.1% of all colorectal cancers.
• Incidence in that group rose by about 0.5% a year, reaching nearly 7 cases per 100,000 person-years.
• Nearly 28% of patients under 50 had metastatic disease at diagnosis, compared with about 20% of older patients.
• In adults aged 50 to 74, rates fell by 1.7% in men and 2.8% in women.
• The increases were mainly in rectal cancers in both sexes and in right-sided colon cancers in young women.

What might explain the rise, and what is unknown?

The authors point to possible contributing factors: changes in diet and lifestyle, rising obesity rates, and early-life environmental exposures affecting the gut microbiome. They add that no single cause can fully explain the trend. That fits an analysis in the All of Us research programme titled “Traditional Risk Factors Are Not Associated with the Rise of Early-Onset Colorectal Cancer”.

The same dataset also shows the opposite trend in older adults: rates fell among 50 to 74 year olds. The overall picture is therefore not one of a uniform increase across ages, and the registry data on their own cannot say why the two groups diverge.

Absolute numbers keep this in proportion. Nearly 7 per 100,000 person-years is a low rate, and 0.5% a year is a slow rise. The finding matters because of the shift in age and the higher share of metastatic disease at diagnosis, not because early-onset disease is common.

Registries cannot capture the individual picture: family history, symptoms over time, or changes in a person’s own bloods. Those rarely meet in a single record.

The bottom line

• Registry data on 96,410 Swiss cases (1980 to 2021) show under-50 incidence rising about 0.5% a year, to nearly 7 per 100,000 person-years.
• Nearly 28% of patients under 50 had metastatic disease at diagnosis, versus about 20% of older patients; rates fell in 50 to 74 year olds.
• Diet, obesity and early-life exposures are proposed, but the authors say no single cause fully explains the rise.