The trial, led by researchers at UCL and UCLH, found that just nine weeks of treatment with pembrolizumab before surgery led to strong and lasting responses in patients with stage two or three colorectal cancer.

No Cancer Recurrence After Nearly Three Years

Early results showed that 59% of patients had no detectable cancer after completing immunotherapy and undergoing surgery. Now, after 33 months of follow-up, none of the patients have experienced a relapse.

This includes both patients whose tumors completely disappeared and those who still had small traces of cancer after treatment. In all cases, the remaining cancer did not grow or spread over time.

This outcome stands in contrast to standard care, where about 25% of patients treated with surgery followed by chemotherapy are expected to see their cancer return within three years. The findings suggest that starting with immunotherapy may offer longer-lasting protection.

Personalized Blood Tests May Predict Treatment Success

Researchers also explored why the treatment worked so well and how to identify patients most likely to benefit. By analyzing blood samples, they developed personalized tests that can detect whether cancer DNA is still present in the bloodstream.

These tests may allow doctors to determine early on whether the treatment has been successful.

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.”

Understanding Colon Cancer Risk and Survival

Bowel cancer is the fourth most common cancer in the UK, with about 44,000 new cases each year. While it primarily affects older adults, diagnoses among people under 50 have been rising.

Outcomes depend heavily on how early the cancer is detected. Around 90% of patients with stage one bowel cancer survive at least five years. Survival drops to 65% at stage three and just 10% at stage four. Some tumor types are also more likely to resist treatment and return.

Trial Details and Patient Group

The NEOPRISM-CRC trial included 32 patients with stage two or three colorectal cancer and a specific genetic subtype (MMR deficient/MSI-high bowel cancer). This subtype accounts for about 10-15% of such cases, or roughly 2,000-3,000 patients each year in the UK.

Participants received up to nine weeks of pembrolizumab before undergoing surgery, instead of the usual approach of surgery followed by several months of chemotherapy. They were then monitored over time.

The latest findings were presented at the American Association for Cancer Research (AACR) Annual Meeting 2026 in San Diego. The study involved multiple UK hospitals, with UCL and UCLH leading the research and biotech company Personalis contributing to the analysis.

Why Immunotherapy Works So Well

Scientists also gained new insights into how immunotherapy produces these lasting effects.

Professor Marnix Jansen 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 when tumor DNA disappeared from the blood, patients were far more likely to remain cancer-free long term.

Yanrong Jiang, first author of the study, 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 Story Highlights Real-World Impact

Christopher Burston, a 73-year-old patient from Portland, Dorset, was diagnosed with colorectal cancer in February 2023 after routine screening detected blood in his stool.

He 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.”

Soon after his diagnosis, he was offered the chance to join the NEOPRISM trial and chose to participate, traveling to London for treatment.

He received three doses of immunotherapy over nine weeks before undergoing surgery in May 2023. His recovery was smooth, with minimal side effects.

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.”

Nearly three years later, he remains cancer-free and has returned to his normal routine.

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.”