Groundbreaking Bowel Cancer Trial Had Zero Relapses for Patients After 33 Months

A small but substantial tweak to the treatment regime of bowel cancer demonstrated remarkable improvements in survival almost 3 years after surgery.

Changing the kind of drug and the delivery window showed substantial improvements over the previous pairing, and build on earlier results showing that the drug led to major tumor shrinkage in patients with stage 2 or 3 bowel cancer.

These latest findings, to be presented at the American Association for Cancer Research (AACR) Annual Meeting 2026 in April, make up the results from the NEOPRISM-CRC clinical trial led by a team from University College London and UCL Hospital.

Patients were treated with a short course of the immunotherapy drug pembrolizumab before surgery instead chemotherapy after surgery. Initial results indicated that 59% of patients had no signs of disease after treatment with pembrolizumab and their operation.

Now 33 months later, none of the treated patients have experienced a return of their cancer. This includes those who had no signs of cancer after treatment and those who still had small amounts remaining, which did not grow or spread during follow-up.

“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 Dr. Kai-Keen Shiu, Chief Investigator of the trial from UCL Cancer Institute and a Consultant Medical Oncologist at UCLH.

It’s expected that around 25% of patients who have the standard surgery and post-op chemotherapy will relapse after 3 years, but this study suggests that a short course of immunotherapy before surgery can provide more durable, long-lasting cancer control for this type of high-risk bowel cancer.

Alongside the survival data, researchers analyzed blood samples to better understand why the treatment is so effective and how to identify those most likely to benefit. They designed personalized blood tests that can show early on whether the treatment had worked and whether any cancer was still present in the bloodstream.

“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,” Dr. Shiu added. “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 around 44,000 cases a year. In the United States, bowel cancer (also referred to as colorectal cancer) is the third most common cancer diagnosis and the second leading cause of cancer-related death for both men and women. For adults under 50, it is now the number one cause of cancer-related mortality.

Like many cancers, if bowel cancer is caught early, the chances of a positive outcome are high. 9 in 10 patients treated for stage 1 bowel cancer survive for 5 years or more, but specific sub-types of tumors don’t respond as well to treatment and are more likely to return. Five-year survival falls to 65% in stage 3 and 10% in stage 4 bowel cancer.

The NEOPRISM-CRC trial saw 32 patients recruited with stage 2 or 3 bowel cancer and a certain genetic profile (MMR deficient/MSI-high bowel cancer) borne by around 10% to 15% of bowel cancer patients from 5 hospitals around the UK.