A groundbreaking clinical trial has achieved what oncologists are calling a potential paradigm shift in colon cancer treatment: after nearly three years of follow-up, none of the patients who received experimental immunotherapy before surgery have seen their cancer return.

The NEOPRISM-CRC trial results, published in Nature Medicine and presented at recent medical conferences, represent a stark departure from conventional treatment protocols. Instead of the standard approach of surgery followed by chemotherapy, 32 patients with stage 2 or 3 colorectal cancer received just nine weeks of treatment with pembrolizumab before surgery.

The drug worked so effectively that 59% of patients had no detectable cancer after completing immunotherapy and undergoing surgery. More remarkably, after extended follow-up, none of the patients have experienced a relapse, according to the research team led by University College London.

“Seeing that no patients have experienced a cancer recurrence after this extended follow-up period is extremely encouraging and strengthens our confidence that pembrolizumab offers significant promise for improving outcomes in patients with high-risk bowel cancers,” said Dr. Kai-Keen Shiu, Chief Investigator of the trial from UCL Cancer Institute and Consultant Medical Oncologist at University College London Hospitals.

The implications are significant. According to published cancer research, patients with similar genetic profiles typically face recurrence rates of approximately 25% within three years using traditional treatment approaches. The new immunotherapy-first strategy appears to offer substantially better protection against cancer returning.

Targeting Genetic Vulnerabilities

The trial focused on patients with tumors representing about 10% to 15% of bowel cancer cases. These cancers have a specific genetic profile called MMR-deficient or MSI-high, indicating a faulty DNA repair system that creates numerous genetic mutations.

Scientists hypothesized that this genetic characteristic, typically considered problematic, could actually work in patients’ favor. The high number of mutations makes these tumors more visible to the immune system, potentially making immunotherapy drugs like pembrolizumab more effective at finding and attacking cancer cells.

The research team, registered under clinical trial NCT03376659, developed sophisticated monitoring tools to track treatment success. By analyzing blood samples, they created personalized tests detecting circulating tumor DNA—genetic material shed by cancer cells into the bloodstream.

“When tumor DNA disappeared from the blood, patients were much more likely to have no cancer remaining after treatment,” explained Professor Marnix Jansen from UCL Cancer Institute. “This blood-based monitoring matched the long-term outcomes we’re observing and suggests we can predict treatment success early in the process.”

Collaborative Research Effort

The study represents a multi-institutional collaboration across the United Kingdom. UCL and University College London Hospitals led the research, with University Hospital Southampton, St. James’s University Hospital in Leeds, and the Christie NHS Foundation Trust in Manchester contributing patient recruitment and biological samples.

Biotechnology company Personalis provided specialized genetic analysis capabilities, while all translational research—the process of applying laboratory discoveries to patient care—was conducted by UCL researchers.

The trial’s design reflects growing recognition that timing of treatments may be as important as the treatments themselves. By administering immunotherapy before surgery, researchers aimed to prime the immune system while the tumor was still intact, potentially creating stronger and more durable immune responses.

“Traditional chemotherapy often suppresses immune function, which may limit the body’s natural ability to recognize and eliminate remaining cancer cells,” said Dr. Shiu. “By leading with immunotherapy, we’re essentially training the immune system to recognize this specific cancer before surgical removal.”

Implications for Cancer Care

The results suggest potential for broader applications beyond this specific genetic subset of colorectal cancers. Similar genetic signatures occur in other cancer types, and researchers are investigating whether comparable approaches might benefit patients with different tumor types.

However, experts emphasize that these remain preliminary results from a relatively small patient group. Larger randomized controlled trials will be necessary to confirm the approach’s effectiveness compared to standard care across diverse patient populations.

The research also highlights the growing importance of genetic testing in cancer treatment selection. Identifying patients with MMR-deficient tumors requires sophisticated pathology testing that may not be universally available.

Cost considerations remain significant, as immunotherapy drugs typically carry substantial price tags compared to traditional chemotherapy regimens. Health systems will need to evaluate cost-effectiveness alongside clinical benefits.

Looking ahead, the research team plans to expand the trial to include additional patients and extend follow-up periods. They’re also investigating optimal treatment durations and exploring combination approaches that might benefit patients whose tumors don’t have the specific genetic vulnerabilities targeted in this study.

“These results provide crucial biological insights into how we might revolutionize cancer treatment by working with, rather than against, the body’s natural defense systems,” Professor Jansen noted. “We’re optimistic about the potential for personalized immunotherapy approaches across multiple cancer types.”

The findings represent a significant step toward precision cancer medicine, where treatment selection is guided by individual tumor genetics rather than one-size-fits-all protocols.