All 32 bowel cancer patients cancer-free nearly 3 years after pre-surgery immunotherapy

All participants in a trial of bowel cancer patients stayed cancer-free nearly three years after an experimental treatment.

Researchers at University College London and UCL Hospitals led the study, which tested immunotherapy before surgery. The trial involved 32 patients with stage 2 or 3 bowel cancer whose tumors had an MMR-deficient or MSI-high genetic profile. This profile occurs in 10% to 15% of bowel cancer cases and signals a faulty DNA repair system, the researchers said.

The patients received pembrolizumab for up to nine weeks before surgery instead of standard post-surgery chemotherapy. Early results showed the drug eliminated all signs of cancer in 59% of cases by surgery time. Now, 33 months later, none of the 32 patients has had cancer return, even those with small traces left after surgery that did not grow or spread.

"Seeing that no patients have experienced a cancer recurrence after almost three years of follow-up is extremely encouraging, and strengthens our confidence that pembrolizumab is a safe and highly effective treatment to improve outcomes in patients with high-risk bowel cancers," said chief investigator Dr. Kai-Keen Shiu, a consultant medical oncologist at UCLH and associate professor at UCL.

Standard surgery followed by chemotherapy leads to cancer return in about 25% of similar patients within three years, the study found.

The team used personalized blood tests to track tumor DNA fragments in the blood and gauge treatment response before surgery. "When tumor DNA disappeared from the blood, patients were much more likely to have no cancer remaining, and this matched the long-term results we’re now seeing," said first author Yanrong Jiang, a clinical PhD student at the UCL Cancer Institute.

The trial had limits as a small study of 32 patients with a specific genetic subset, so results may not apply broadly. Longer follow-up is needed to confirm no late recurrences.

Still, the researchers expressed hope for personalized medicine. "What is particularly exciting is that we now may be able to predict who will respond to the treatment using personalized blood tests and immune profiling," Shiu said. "These tools could help us tailor our approach, identifying patients who are doing well and may need less therapy before and after surgery."

The findings were presented last month at the American Association for Cancer Research Annual Meeting 2026 in San Diego.