A new clinical trial suggests that immunotherapy given before surgery may dramatically improve outcomes for certain colorectal cancer patients. In the NEOPRISM-CRC study, patients treated with a short course of immunotherapy instead of chemotherapy after surgery remained cancer-free for nearly three years.
The trial, led by researchers at UCL and UCLH, found that just nine weeks of pembrolizumab before surgery produced strong and durable responses in patients with stage 2 or 3 colorectal cancer.
The cancer has not returned even after nearly 3 years.
Initial results showed that 59% of patients had no detectable cancer after completing immunotherapy and undergoing surgery. After 33 months of follow-up, none of the patients currently experienced recurrence.
This includes both patients whose tumors have completely disappeared and patients who have slight traces of cancer remaining after treatment. In both cases, the remaining cancer did not grow or spread over time.
This contrasts with standard treatment, where about 25% of patients who receive chemotherapy after surgery are expected to have their cancer return within three years. The results of this study suggest that starting immunotherapy may provide longer-term protective effects.
Personalized blood tests may predict treatment success
The researchers also investigated why the treatment was so successful and how to identify patients who would benefit most. They have developed a separate test that can detect whether cancer DNA is still present in the bloodstream by analyzing a blood sample.
These tests may allow doctors to determine early whether treatment has been successful.
Dr Kai Keen Siu, lead investigator of the trial at UCL Cancer Research Institute and consultant clinical oncologist at UCLH, said: “After nearly three years of follow-up, it is very encouraging that the patient has not experienced cancer recurrence and strengthens our confidence that pembrolizumab is a safe and effective treatment to improve outcomes for patients with high-risk colorectal cancer.”
“Of particular interest is the possibility of using personalized blood tests and immune profiling to predict who will respond to treatment. These tools could help us tailor our approach by identifying patients who are doing well and may require less treatment before and after surgery, and those who require additional treatment and are at high risk of disease progression or recurrence.”
Understanding colon cancer risk and survival
Bowel cancer is the fourth most common cancer in the UK, with around 44,000 new cases occurring each year. It primarily affects older people, but diagnosis in people under 50 is also increasing.
Outcomes largely depend on how early the cancer is detected. Approximately 90% of patients with stage 1 colorectal cancer survive at least 5 years. Survival rates drop to 65% in stage 3 and only 10% in stage 4. Some types of tumors resist treatment and are more likely to recur.
Trial details and patient groups
The NEOPRISM-CRC trial enrolled 32 patients with stage 2 or 3 colorectal cancer and a specific genetic subtype (MMR-deficient/MSI-high bowel cancer). This subtype accounts for approximately 10-15% of such cases and occurs in approximately 2,000-3,000 patients each year in the UK.
Participants received up to nine weeks of pembrolizumab before undergoing surgery, rather than the usual approach of months of chemotherapy after surgery. They were then monitored over time.
The latest research results were presented at the American Association for Cancer Research (AACR) 2026 Annual Meeting in San Diego. The study involved several UK hospitals, with UCL and UCLH leading the research and biotechnology company Personalis contributing to the analysis.
Why is immunotherapy so effective?
Scientists also gained new insights into how immunotherapy produces these long-lasting effects.
Professor Marnix Jansen, from the UCL Institute of Cancer Research and UCLH, said: “These results not only confirm the durability of the response observed almost three years ago, but also provide important biological insights into why immunotherapy is so effective in this setting.”
Researchers found that once tumor DNA disappeared from the blood, patients were much more likely to be cancer-free in the long term.
Yanrong Jiang, lead author of the study, said: “As a research team, we were thrilled to be able to follow patients so closely using personalized blood tests. Once tumor DNA disappears from the blood, patients are much more likely to have no residual cancer, which is consistent with the long-term results we are currently seeing.”
“We also found that immune profiling from tumor tissue can help predict response before patients begin their first treatment cycle. We hope these tests will be used to guide treatment decisions in a more practical and timely manner.”
Patient stories highlight real-world impact
Patient Christopher Burston, 73, from Portland, Dorset, was diagnosed with colorectal cancer in February 2023 after blood was detected in his stool during a routine test.
He said: “One person came back with signs of blood in his stool. I went for further tests and a colonoscopy found cancer in my intestines.”
Shortly after his diagnosis, he was offered the opportunity to take part in the NEOPRISM trial, which he chose to do and traveled to London for treatment.
He received three rounds of immunotherapy over nine weeks before undergoing surgery in May 2023. Side effects were minimal and he recovered smoothly.
“The results of the surgery, the doctors said, essentially meant that the cancer had melted away. The immunotherapy was almost instantaneous. When I looked at the images from my first colonoscopy, it turned out to be a really, really big lump. So, like I said, it was no small thing, and I was diagnosed with stage 3 cancer.”
Almost three years later, he remains cancer-free and has returned to his normal daily life.
Christopher said: “My recovery was smooth, I had no problems and since then my health has almost returned to normal. I feel very lucky to have gotten to the point where the main problem is age and not cancer or disease.”
