A small but striking clinical trial in the U.K. has recorded zero cancer relapses among bowel cancer patients who received immunotherapy before surgery — nearly three years after treatment ended. The results, presented at the American Association for Cancer Research meeting in San Diego, suggest that for a specific group of patients, this approach may dramatically outperform standard care.
At a glance
- Pre-surgery immunotherapy: Patients received up to nine weeks of pembrolizumab before bowel surgery, replacing the conventional sequence of surgery followed by three to six months of chemotherapy.
- Zero relapses: After 33 months of follow-up, none of the 32 trial participants — including some who had residual cancer after treatment — had seen their cancer return.
- MMR-deficient bowel cancer: The trial targeted patients with a specific genetic profile found in roughly 10–15% of stage two or three bowel cancer cases, representing around 2,000–3,000 U.K. diagnoses per year.
What the trial found
The NEOPRISM-CRC trial, led by University College London (UCL) and University College London Hospitals NHS Foundation Trust (UCLH), enrolled 32 patients with stage two or three bowel cancer who carried a genetic marker known as MMR deficiency, or MSI-high status. Participants were recruited across five U.K. hospitals.
After nine weeks of pre-operative pembrolizumab, 59% of patients showed no detectable signs of disease by the time they reached surgery. That alone was a notable result. What researchers have now confirmed is that after nearly three years, not a single patient in the group has relapsed — including those who still had small amounts of residual cancer after their operation.
By contrast, standard treatment — surgery followed by post-operative chemotherapy — sees roughly one in four patients experience a recurrence within three years. The difference is significant enough that the trial team described the findings as “extremely encouraging.”
What one patient experienced
Christopher Burston, 73, from Portland, Dorset, was diagnosed with bowel cancer in February 2023 C.E. following routine screening. He received three doses of immunotherapy over nine weeks, then had surgery.
“The outcome of the surgery was essentially that the cancer had melted away — these were the doctor’s words,” Burston said. “The immunotherapy had had an almost immediate effect.”
More than three years on, he remains cancer-free. “I feel very lucky that I’ve reached the stage where my main problem is age rather than cancer or any illness,” he said. “I am able to play guitar, tend my garden and walk the dog very much as before.”
His account reflects a broader pattern in the trial: patients who might have faced months of chemotherapy and its side effects instead moved through a shorter, targeted treatment window and into recovery.
Why the genetic profile matters
Pembrolizumab is a checkpoint inhibitor — a class of drugs that works by releasing the immune system’s natural brakes, allowing it to recognize and attack cancer cells. It does not work equally well across all cancers, and that is where the MMR-deficient genetic profile becomes critical.
Tumors with this profile tend to carry a high number of mutations, making them more visible to the immune system. Research into checkpoint inhibitors has consistently shown stronger responses in these hypermutated cancers, which is why the NEOPRISM-CRC trial focused specifically on this subgroup.
Dr. Kai-Keen Shiu, chief investigator from the UCL Cancer Institute and consultant medical oncologist at UCLH, said the team may now be able to go further — predicting which patients will respond best using personalized blood tests and immune profiling. “These tools could help us tailor our approach,” he said, “identifying patients who are doing well and may need less therapy versus patients at higher risk who need additional treatment.”
The road ahead
The NEOPRISM-CRC results are promising, but they come with important caveats. The trial involved just 32 patients — a small sample — and the genetic profile it targeted accounts for only a fraction of all bowel cancer cases. Larger trials will be needed before this approach can become a standard treatment pathway.
Researchers are also cautiously optimistic that the approach could eventually be extended to other bowel cancer patients without this specific genetic marker, though that work is still in early stages. Cancer Research U.K. notes that immunotherapy for bowel cancer is still a developing field, with most patients currently ineligible for these drugs under standard protocols.
The findings were presented at the 2025 C.E. AACR Annual Meeting. The trial was funded in part through the National Institute for Health and Care Research, with support from Merck, the manufacturer of pembrolizumab. Researcher funding relationships like this are standard in pharmaceutical trials and are disclosed in the published findings — something worth bearing in mind when interpreting the results, even as the outcomes remain striking.
Bowel cancer is the fourth most common cancer worldwide, with over 1.9 million new cases recorded globally in 2022 C.E. A treatment that eliminates the need for post-operative chemotherapy in even a subset of patients would meaningfully reduce both the physical burden of treatment and the long-term strain on health systems.
Read more
For more on this story, see: The Independent
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