The exercise trial with a drug-sized effect

In a phase 3 randomised trial of 889 colon cancer patients, a three-year structured exercise programme was associated with a 28% lower risk of recurrence and a 37% lower risk of death than health education alone. Median follow-up was 7.9 years. This is an effect size that would be reimbursed if it arrived in a vial.

What did the CHALLENGE trial show?

The CHALLENGE trial, published in the New England Journal of Medicine in 2025 and presented at ASCO, randomised 889 patients who had completed adjuvant chemotherapy for colon cancer. Half received a structured exercise programme delivered with a physical activity consultant, twice monthly for six months and monthly thereafter. Half received health education materials.

Five-year disease-free survival was 80.3% in the exercise group against 73.9% in the education group. Eight-year overall survival was 90% against 83%, a hazard ratio of 0.63 for death. In absolute terms: 93 recurrences versus 131, and 41 deaths versus 66.

Because this was a randomised controlled trial rather than an observational cohort, the design supports a causal reading in a way that most exercise research does not. That is the part that makes it unusual.

Why does a randomised design change the argument?

Almost everything the public hears about exercise and disease comes from observational studies, where people who exercise more also tend to smoke less, sleep better and have more money. Those studies can only report association, and a reasonable sceptic can always argue the benefit belongs to something else.

CHALLENGE removed that objection by assigning the intervention. When a structured exercise programme is randomised and the exercise group has fewer recurrences and fewer deaths, the ambiguity that hangs over the rest of the exercise and longevity literature is largely gone.

It also reframes adherence. If exercise is an intervention with a measurable effect size, then how much of it a patient actually does becomes a clinical variable, in the same way that adherence to a prescription is. Self-reported activity is a poor instrument for that. Continuous measurement is a better one.

The bottom line

• In 889 randomised colon cancer patients, structured exercise showed 80.3% five-year disease-free survival against 73.9% for health education, a 28% risk reduction.
• Eight-year overall survival was 90% against 83%, a 37% reduction in risk of death.
• This is a phase 3 RCT in colon cancer specifically, so it supports causal inference rather than association alone, but does not automatically generalise to other cancers.