By Budi Oetomo Narendra 
Patients battling a specific, aggressive form of bowel cancer have shown remarkable resilience, remaining free of recurrence for almost three years after undergoing a novel, short course of immunotherapy administered prior to surgery. These groundbreaking findings stem from the NEOPRISM-CRC clinical trial, spearheaded by researchers at University College London (UCL) and University College London Hospitals NHS Foundation Trust (UCLH), offering a potent new paradigm in cancer treatment. The latest results, which significantly extend earlier observations, are slated for presentation at the prestigious American Association for Cancer Research (AACR) Annual Meeting 2026, highlighting a potential shift in the standard of care for a challenging disease.
Groundbreaking Durability: Zero Recurrences After 33 Months
The core of these extended findings reveals an unprecedented level of treatment durability. After an average follow-up period of 33 months, none of the patients participating in the NEOPRISM-CRC trial had experienced a return of their cancer. This extraordinary outcome held true for all participants, encompassing both those who showed no detectable signs of disease post-treatment and surgery, and those who still presented with minor, residual amounts of cancer. Crucially, in the latter group, the remaining cancer did not progress, grow, or metastasize throughout the follow-up period.
This zero-recurrence rate stands in stark contrast to conventional treatment approaches for similar patient cohorts. Typically, around 25% of patients treated with the standard regimen of surgery followed by chemotherapy are expected to relapse within a three-year timeframe. The NEOPRISM-CRC trial’s results strongly suggest that a strategically timed, short course of immunotherapy administered before surgery — a neo-adjuvant approach — may offer a significantly more durable form of cancer control for this specific subtype of bowel cancer, surpassing the efficacy of traditional post-operative chemotherapy. This sustained period of disease freedom offers immense hope, not only in terms of survival but also in the potential for improved quality of life, sparing patients from the gruelling side effects of prolonged chemotherapy.
The NEOPRISM-CRC Trial: A Paradigm Shift in Treatment Strategy
The NEOPRISM-CRC trial initially garnered significant attention when preliminary data indicated that a nine-week course of the immunotherapy drug pembrolizumab administered prior to surgery induced major tumor shrinkage in individuals diagnosed with stage two or three bowel cancer. Earlier reported data underscored this efficacy, showing that a remarkable 59% of patients achieved no detectable signs of disease following their pembrolizumab treatment and subsequent planned bowel cancer surgery. The latest 33-month recurrence-free survival data builds upon this foundation, validating the initial promise with long-term evidence of efficacy.
The trial specifically enrolled 32 patients diagnosed with stage two or three bowel cancer who possessed a particular genetic signature: mismatch repair deficient (MMR-deficient) or microsatellite instability-high (MSI-high) bowel cancer. This genetic make-up is present in approximately 10-15% of individuals with stage two or three bowel cancer, translating to roughly 2,000 to 3,000 new cases annually in the UK alone. This specific subtype is known to be particularly amenable to immunotherapy due to its high mutational burden, making cancer cells more recognizable to the immune system.
Instead of the conventional pathway of surgery followed by three to six months of chemotherapy, participants in the NEOPRISM-CRC trial received up to nine weeks of pembrolizumab. This innovative pre-surgical (neo-adjuvant) treatment aims to reduce tumor size and eliminate micrometastases before the primary tumor is surgically removed, potentially rendering the surgery more effective and reducing the likelihood of recurrence. Following surgery, patients were meticulously monitored over time to track their long-term outcomes. The latest phase of this ongoing trial, presented previously at AACR in San Diego, California, and now with extended follow-up for the 2026 meeting, was led by UCL and UCLH. Key collaborators in patient recruitment and sample collection included University Hospital Southampton, St. James’s University Hospital in Leeds, and the Christie NHS Foundation Trust in Manchester, with all translational research conducted by UCL and biotechnology company Personalis.
Understanding Bowel Cancer and the Promise of Immunotherapy
Bowel cancer, also known as colorectal cancer, remains a significant public health concern globally and is the fourth most common cancer in the UK, with approximately 44,000 new cases diagnosed each year. While it predominantly affects older adults, there has been a concerning rise in incidence rates among individuals younger than 50 in recent decades, prompting increased awareness and screening efforts.
Survival outcomes for bowel cancer are highly dependent on the stage at which the cancer is detected. Early diagnosis significantly improves prognosis; around nine out of ten people treated for stage one bowel cancer survive for at least five years. However, this figure drops considerably for more advanced stages, with five-year survival falling to 65% for stage three bowel cancer and a stark 10% for stage four metastatic disease. Furthermore, certain tumor subtypes respond less effectively to conventional treatments and are more prone to recurrence, highlighting the critical need for more effective therapies like those being explored in the NEOPRISM-CRC trial.
Pembrolizumab, marketed as Keytruda, is a monoclonal antibody that functions as a PD-1 (programmed death-1) immune checkpoint inhibitor. It works by blocking the PD-1 pathway, which cancer cells often exploit to evade detection and destruction by the body’s immune system. By inhibiting PD-1, pembrolizumab effectively "unleashes" the immune system’s T-cells, allowing them to recognize and attack cancer cells more effectively. This mechanism is particularly potent in MMR-deficient/MSI-high cancers because these tumors accumulate a large number of mutations, making them highly immunogenic—meaning they present more abnormal proteins (neoantigens) that the activated immune system can target.
Pioneering Personalized Diagnostics: Guiding Future Treatment
Beyond demonstrating remarkable efficacy, the NEOPRISM-CRC trial has also made significant strides in personalized medicine. Researchers meticulously analyzed blood samples to uncover the biological mechanisms underpinning the treatment’s success and to identify biomarkers that could predict which patients are most likely to benefit. This led to the development of sophisticated, personalized blood tests designed to offer early indications of treatment response and detect minute traces of cancer cells circulating in the bloodstream, known as circulating tumor DNA (ctDNA).
Dr. Kai-Keen Shiu, the Chief Investigator of the trial from UCL Cancer Institute and a Consultant Medical Oncologist at UCLH, expressed profound optimism regarding these advancements. "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," Dr. Shiu stated. He further emphasized the diagnostic breakthroughs: "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."
Professor Marnix Jansen, a clinician scientist and consultant histopathologist leading the translational research from UCL Cancer Institute and UCLH, underscored the scientific depth of the findings. "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," Professor Jansen commented. The research team discovered that dynamic changes in tumor DNA levels within the bloodstream served as a highly accurate proxy for patient response. The complete disappearance of tumor DNA from the blood was strongly correlated with the absence of any remaining cancer cells in the patient.
Yanrong Jiang, the first author of the latest abstract and a clinical PhD student at the UCL Cancer Institute, highlighted the practical implications of these diagnostic tools. "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," Jiang explained. "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, potentially sparing some patients from unnecessary treatments and directing others to more intensive therapies if needed."
A Beacon of Hope: Christopher Burston’s Journey
The profound impact of the NEOPRISM-CRC trial is perhaps best illustrated through the personal experiences of patients like Christopher Burston. Christopher, a 73-year-old resident of Portland, Dorset, was diagnosed with bowel cancer in February 2023 after participating in routine screening. His diligent use of postal bowel screening kits, a crucial early detection tool, eventually flagged a positive result.
"One came back with indications of blood in my stool," Christopher recalled. "I went through further tests, and it was at the colonoscopy that they identified a cancer in my bowel." A few weeks after his stage 3 diagnosis, Christopher’s oncologist presented him with the opportunity to join the NEOPRISM clinical trial, which was investigating pre-surgical immunotherapy. Despite the necessity of traveling to London for treatment, Christopher chose to enroll and was referred to UCLH.
He received three doses of immunotherapy over a nine-week period before undergoing surgery in May 2023. Christopher experienced minimal side effects from the immunotherapy and recovered remarkably well after a week in the hospital. The outcome of his surgery was nothing short of miraculous. "The outcome of the surgery was essentially that the cancer had melted away, these were the doctor’s words," Christopher recounted. "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, having returned to his normal activities while diligently attending regular follow-up appointments. His journey stands as a powerful testament to the trial’s success. "The recovery went fine. I didn’t have any problems. And since then, I’ve been feeling pretty much back to normal," Christopher affirmed. "I feel very lucky that I’ve reached the stage where my main problem is age rather than cancer or any illness."
Broader Implications and The Path Ahead
The findings from the NEOPRISM-CRC trial carry immense implications for the future of bowel cancer care. The demonstrated long-term recurrence-free survival in a high-risk patient group suggests that neo-adjuvant immunotherapy could fundamentally alter treatment algorithms, potentially reducing the need for aggressive post-operative chemotherapy and its associated toxicities. This could significantly improve patient quality of life, allowing for faster recovery and return to normal activities, as exemplified by Christopher Burston.
From a public health perspective, redefining the standard of care for this specific bowel cancer subtype could lead to better overall survival rates and a reduction in the long-term burden of recurrence. While immunotherapy drugs like pembrolizumab are costly, the potential to shorten overall treatment duration and prevent expensive, intensive treatments for recurrent disease could offer a compelling health economic argument in the long run.
The development of personalized blood tests and immune profiling tools is equally transformative. These diagnostics could usher in an era of true precision medicine in oncology, allowing clinicians to identify responders early, monitor treatment effectiveness in real-time, and tailor therapeutic strategies more effectively. This adaptive approach could optimize patient outcomes, minimize unnecessary treatments, and allocate resources more efficiently.
However, the path ahead involves further rigorous investigation. While the NEOPRISM-CRC trial’s results are highly promising, it was a relatively small, single-arm study. The next crucial step will be to validate these findings in larger, randomized controlled trials that compare neo-adjuvant immunotherapy directly against the current standard of care. Such trials will be essential to definitively establish this approach as the new benchmark. Furthermore, research will continue to explore whether similar benefits can be extended to other subtypes of bowel cancer or even other solid tumors, and how to ensure equitable access to these advanced therapies and diagnostic tools across diverse healthcare systems. The NEOPRISM-CRC trial represents a significant leap forward, illuminating a future where advanced diagnostics and targeted immunotherapy work in concert to offer durable control and renewed hope for patients facing high-risk bowel cancer.
