Bowel cancer “melted away” after immunotherapy, then stayed away

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.

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 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.