All participants in a trial of bowel cancer patients remained cancer-free nearly three years after receiving an experimental treatment.
Led by researchers at University College London and UCL Hospitals, the study suggests that a short course of immunotherapy before surgery could produce better results than the current standard of care for certain patients.
The trial focused on 32 patients with stage 2 or 3 bowel cancer. These patients had tumors with a specific genetic profile called MMR-deficient or MSI-high, according to a press release.
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This profile, which is found in about 10% to 15% of bowel cancer cases, indicates a faulty DNA repair system in the body, the researchers noted. However, scientists hypothesized, that could make it easier for immunotherapy drugs to find and attack the tumors.
Instead of receiving standard chemotherapy after surgery, these patients were given a drug called pembrolizumab before their operations. The treatment lasted up to nine weeks.
Early data showed that the drug shrank tumors so effectively that 59% of patients had no signs of cancer left by the time they went in for surgery.
The latest data confirms that 33 months later, none of those patients have seen a return of the disease, including those who still had small traces of cancer remaining after surgery that never grew or spread again.
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“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, in the release.
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With the traditional approach of surgery followed by chemotherapy, about 25% of patients with this genetic profile would see their cancer return within three years, according to the study.
The research team also used personalized blood tests to monitor the patients. These tests look for tiny fragments of tumor DNA in the bloodstream, allowing doctors to determine whether the treatment was working before the surgery.
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“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, in the release.
The study did have limitations, the researchers noted. It was a small trial with only 32 people and only looked at a specific genetic subset of patients, which means the results may not apply to everyone with bowel cancer.
Doctors also need to follow the patients for a longer period to ensure that the cancer doesn’t return, they added.
Even so, the researchers shared their optimism about the future of personalized care.
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“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 results were presented at the American Association for Cancer Research (AACR) Annual Meeting 2026 in San Diego last month.
