A groundbreaking clinical trial led by researchers at University College London (UCL) and University College London Hospitals (UCLH) has unveiled promising new results that may revolutionize the treatment landscape for a subset of bowel cancer patients. The NEOPRISM-CRC trial investigated the efficacy of administering a short course of immunotherapy before surgical intervention, bypassing the conventional post-operative chemotherapy regimen. This novel approach, focused on patients with stage two or three bowel cancer exhibiting mismatch repair deficiency (MMR deficient) or microsatellite instability-high (MSI-high) genetic profiles, demonstrated remarkable long-term cancer remission rates after nearly three years of follow-up.
Immunotherapy with the drug pembrolizumab—a checkpoint inhibitor targeting the PD-1 receptor—was administered over nine weeks prior to surgery to 32 enrolled patients. Early findings from the trial, previously reported, indicated a major shrinkage in tumor size, with 59 percent of these patients showing no detectable disease immediately following treatment and surgical resection. The sustained effectiveness of this intervention has now been firmly established, as none of the treated patients have experienced disease recurrence over 33 months. This represents a significant improvement compared to the approximate 25 percent relapse rate observed after the standard treatment of surgery followed by chemotherapy.
The sustaining disease-free status of patients, irrespective of whether microscopic residual cancer remained post-treatment, suggests that pre-operative immunotherapy induces a durable anti-tumor immune response that effectively controls or eradicates residual malignant cells. This is especially relevant to the MMR deficient/MSI-high subgroup, accounting for roughly 10-15 percent of stage two and three bowel cancers and characterized by a high mutational burden which renders these tumors particularly susceptible to immune checkpoint blockade.
A critical facet of the NEOPRISM-CRC trial has been the integration of innovative liquid biopsy techniques. Researchers collected and analyzed serial blood samples to detect circulating tumor DNA (ctDNA), providing an early and dynamic biomarker of treatment efficacy. Personalized blood tests were developed, successfully correlating the disappearance of tumor-specific DNA fragments from circulation with positive long-term outcomes. This approach not only affords clinicians a minimally invasive window into tumor dynamics during and after therapy but also facilitates early identification of patients unlikely to fully respond and therefore in need of intensified treatment.
In parallel, immune profiling of tumor biopsy samples prior to treatment initiation allowed scientists to decode the immunological landscape predictive of therapeutic response. These analyses revealed key features of the tumor microenvironment and immune cell infiltration patterns that could inform patient stratification. By combining molecular and immunological biomarkers, the trial sets a precedent for truly personalized cancer therapy—enabling treatment intensification or de-escalation tailored to individual patient responses.
Clinician scientists involved emphasize the clinical implications of these findings, heralding pembrolizumab given pre-operatively as a safe and highly effective alternative to protracted chemotherapy in a genetically defined patient population. The profound reduction in treatment-related toxicity and improved quality of life associated with foregoing chemotherapy cannot be overstated, especially considering the older demographics typically affected by bowel cancer.
Bowel cancer remains the fourth most common cancer in the UK with an incidence of around 44,000 cases annually. While early-stage disease boasts a favorable prognosis—with approximately 90 percent five-year survival for stage one—the outlook declines steeply for stage three and IV cancers, where five-year survival rates drop to 65 percent and 10 percent, respectively. The NEOPRISM-CRC trial focused on stage two and three cancers with mismatch repair deficiency, targeting a subgroup presently limited in therapeutic options.
One of the trial participants, Christopher Burston, aged 73, exemplifies the transformative impact of immunotherapy within this context. Diagnosed during routine screening, he underwent nine weeks of pembrolizumab followed by surgery. His remarkable clinical response—described by clinicians as the tumor having “melted away”—was achieved without the debilitating side effects commonly seen with chemotherapy. After more than three years, he remains in complete remission and has returned to normal activities, underscoring the real-world benefits of this novel treatment paradigm.
The trial recruitment spanned five UK hospitals, including University Hospital Southampton, St. James’s University Hospital in Leeds, and the Christie NHS Foundation Trust in Manchester. This collaborative effort facilitated comprehensive translational research conducted by UCL and biotech partner Personalis, further advancing the understanding of biological underpinnings responsible for durable responses to immunotherapy.
As the scientific community awaits the formal presentation of these latest data at the upcoming American Association for Cancer Research (AACR) Annual Meeting 2026 in San Diego, the findings emphasize a crucial pivot in bowel cancer management. Instead of relying on adjuvant chemotherapy post-surgery, configuring treatment strategies around neoadjuvant immunotherapy could enhance long-term outcomes, reduce treatment burdens, and move towards precision oncology in colorectal malignancies.
Overall, the NEOPRISM-CRC study advocates for a paradigm shift in treating specific bowel cancer subsets by harnessing the immune system ahead of surgical intervention. Continued development of personalized blood tests and immune profiling techniques will likely optimize patient selection and guide therapeutic decisions, paving the way for broader implementation of immunotherapy as a frontline treatment in this otherwise challenging malignancy.
Subject of Research: People
Article Title: Pre-Operative Immunotherapy with Pembrolizumab Secures Durable Remission in MMR Deficient/MSI-High Bowel Cancer: Long-Term Data from NEOPRISM-CRC Trial
News Publication Date: April 20, 2026
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Keywords:
Cancer immunotherapy, bowel cancer, colorectal cancer, immunotherapy, pembrolizumab, NEOPRISM-CRC trial, microsatellite instability, mismatch repair deficiency, neoadjuvant therapy, liquid biopsy, circulating tumor DNA, personalized medicine
