Patients with a particular form of bowel cancer remained free of recurrence for almost three years after receiving a short course of immunotherapy before surgery, according to new findings from the NEOPRISM-CRC clinical trial led by researchers at UCL and UCLH.
The results, which are due to be presented at the American Association for Cancer Research (AACR) Annual Meeting 2026 in April, extend earlier findings from the trial. Those initial results showed that nine weeks of treatment with the immunotherapy drug pembrolizumab before surgery caused major tumor shrinkage in people with stage two or three bowel cancer.
Earlier data showed that 59% of patients had no detectable signs of disease after pembrolizumab treatment and their planned bowel cancer surgery.
Zero Recurrences After 33 Months
After 33 months of follow-up, none of the patients treated in the trial had experienced a return of their cancer. That was true both for patients who had no signs of cancer after treatment and for those who still had small amounts of disease remaining. In the latter group, the remaining cancer did not grow or spread during follow-up.
By comparison, around 25% of patients treated with the standard approach of surgery followed by chemotherapy are expected to relapse within three years. The findings suggest that giving a short course of immunotherapy before surgery may provide more durable cancer control for this specific type of bowel cancer than the usual combination of surgery and post-operative chemotherapy.
Researchers also studied blood samples to investigate why the treatment worked so well and to find ways of identifying which patients were most likely to benefit. They developed personalized blood tests designed to show early whether treatment had worked and whether traces of cancer were still circulating in the bloodstream.
Dr. Kai-Keen Shiu, Chief Investigator of the trial from UCL Cancer Institute and a Consultant Medical Oncologist at UCLH, said: “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.
“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. These tools could help us tailor our approach, identifying patients who are doing well and may need less therapy before and after surgery versus patients at higher risk of disease progression or relapse who need additional treatment.”
Bowel Cancer Survival Varies by Stage
Bowel cancer is the fourth most common cancer in the UK, with roughly 44,000 new cases diagnosed each year. It continues to affect older adults most often, although rates among people younger than 50 have been rising in recent decades.
As with many cancers, outcomes are much better when bowel cancer is detected early. Around nine in ten people treated for stage one bowel cancer survive for at least five years. However, some tumor sub-types respond less effectively to treatment and are more likely to return. Five-year survival drops to 65% for stage three bowel cancer and 10% for stage four disease.
The NEOPRISM-CRC trial enrolled 32 patients with stage two or three bowel cancer and a particular genetic profile (MMR deficient/MSI-high bowel cancer) at five hospitals across the UK. Around 10-15% of people with stage two or three bowel cancer have this genetic make-up, equivalent to roughly 2,000-3,000 cases each year in the UK.
Instead of undergoing surgery followed by three to six months of chemotherapy, participants received up to nine weeks of pembrolizumab before their bowel surgery. Researchers then continued monitoring them over time.
Personalized Blood Tests Could Guide Treatment
The latest phase of the ongoing trial, presented this month at AACR in San Diego, California, was led by UCL and UCLH. University Hospital Southampton, St. James’s University Hospital in Leeds and the Christie NHS Foundation Trust in Manchester also helped recruit patients and supplied valuable translational samples. All translational work was carried out by UCL and biotechnology company Personalis.
Professor Marnix Jansen, a clinician scientist and consultant histopathologist who is leading the translational research on the trial from UCL Cancer Institute and UCLH, said: “These results not only confirm the durability of responses we saw almost three years ago, but also provide crucial biological insights into why immunotherapy is so effective in this setting.”
Researchers found that changes in tumor DNA in the bloodstream closely reflected how well patients were responding. Disappearance of tumor DNA from the blood was strongly associated with having no cancer remaining.
Yanrong Jiang, first author of the latest abstract and clinical PhD student at the UCL Cancer Institute, said: “As a research team, we were thrilled to be able to follow patients very closely using the personalized blood tests. 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.
“In addition, we also saw that immune profiling from tumor tissue, before patients start their first cycle of treatment, can help to predict response. We hope these tests may be used to guide treatment decisions in a more practical and timely way.”
Patient’s Story
UCLH patient Christopher Burston was diagnosed with bowel cancer in February 2023 after taking part in routine screening. He had completed bowel screening kits sent through the post for several years before one test came back positive.
Christopher, 73, of Portland, Dorset, said: “One came back with indications of blood in my stool. I went through further tests, and it was at the colonoscopy that they identified a cancer in my bowel.”
A few weeks after his diagnosis, Christopher’s oncologist told him he might qualify for the NEOPRISM clinical trial, which was testing immunotherapy before surgery. Although taking part meant traveling to London for treatment, he chose to enroll and was referred to UCLH.
He received three doses of immunotherapy across nine weeks before undergoing surgery in May 2023. Christopher experienced few side effects and recovered well after spending one week in the hospital.
He said: “The outcome of the surgery was essentially that the cancer had melted away, these were the doctor’s words. The immunotherapy had had an almost immediate effect. I saw the images when I had the first colonoscopy and could see it was really quite a substantial lump. So as I say, it wasn’t a minor thing, I was diagnosed with stage 3 cancer.”
More than three years later, Christopher remains cancer-free. He has returned to his normal activities while continuing to attend regular follow-up appointments.
Christopher said: “The recovery went fine. I didn’t have any problems. And since then, I’ve been feeling pretty much back to normal. I feel very lucky that I’ve reached the stage where my main problem is age rather than cancer or any illness.”