People who took part in colorectal cancer screening had a 43 per cent lower risk of dying from the disease, according to long-term data from more than 376,000 people in Sweden. The test involved is one posted to the home.

Why this cancer is unusually suited to screening

Not every cancer is worth screening for, and the reasons colorectal cancer is a good candidate are specific.

Most cases develop from polyps — growths in the bowel wall that are initially benign and take years, often a decade or more, to become malignant. That long window means a test has time to find something, and finding a polyp allows it to be removed before any cancer exists.

This makes colorectal screening different in kind from most cancer screening, which detects disease earlier. Here, some of the benefit comes from preventing the disease from occurring at all — which is why the mortality effect can be as large as it is.

What “43 per cent lower risk” means

This is a relative reduction, and relative figures always sound larger than the absolute change they describe.

If the underlying risk of dying from a disease over a period is, say, one in a hundred, a 43 per cent relative reduction takes it to roughly one in 175. That is a real and worthwhile improvement, and it is not the same as a 43-point drop in anyone’s chance of dying.

There is a second caution. This compares people who participated with people who did not, and participation is a choice. People who return a screening kit differ systematically from those who do not — in age, income, health literacy, and general engagement with healthcare, all of which independently predict outcomes. Analyses adjust for what they can measure, but self-selection is the standard objection to studies of this design, and it usually inflates the apparent benefit somewhat.

The costs on the other side

Screening programmes carry harms as well as benefits, and a paper reporting only the benefit is telling half the story.

A positive home test leads to colonoscopy, an invasive procedure with a small but real rate of complications including bleeding and perforation. Most people referred after a positive result turn out not to have cancer, having spent weeks worrying. And some detected growths would never have caused harm in the person’s lifetime — overdiagnosis, which is harder to quantify here than in some other screening programmes but is not zero.

The reason most health systems run these programmes anyway is that, for this cancer, the balance is unusually favourable. That is a judgement about a population, not a prediction about any individual.

Why Sweden is a good place to measure it

A study of 376,000 people followed over many years is only possible where health data can be linked reliably across a population. The Nordic countries maintain national registries connecting screening records, diagnoses, treatment and deaths, with personal identifiers that allow individuals to be followed for decades.

That infrastructure is why a disproportionate share of the world’s long-term epidemiology comes from this region. It is also why findings from it sometimes transfer imperfectly: a screening programme’s effectiveness depends on uptake, referral pathways and treatment quality, which differ substantially between health systems.

This reports research findings and is not medical advice. Anyone with questions about screening should raise them with their doctor.

Sources

• ScienceDaily — colorectal cancer screening and mortality, Swedish long-term data, 21 August 2026