A small University College London trial found that a brief course of immunotherapy before surgery cleared tumors in many patients with a specific genetic type of bowel cancer, and nearly three years later those participants have seen no return of the disease, with personalized blood tests helping track responses and inform future care.
Researchers treated 32 patients with stage 2 or 3 bowel cancer characterized as MMR-deficient or MSI-high, a genetic signature that makes tumors more visible to the immune system. Rather than the usual route of surgery followed by chemotherapy, patients received pembrolizumab for up to nine weeks before their operations. The idea was to prime the immune response so the body could attack the tumor while it was still in place. It’s a bold flip of the usual script, and it produced striking early signals.
By the time these patients went into surgery, 59% had no detectable cancer left at the tumor site. That tumor shrinkage was dramatic enough to change how many surgeons approached the procedures and how oncologists viewed the role of preoperative therapy. Those immediate results were promising, but what really turned heads was how durable the benefit appeared to be over time.
At about 33 months of follow-up, none of the trial participants had experienced a recurrence of their cancer. That includes people who still had microscopic traces after surgery that never grew or spread again. For context, the more traditional path of surgery followed by chemotherapy typically sees roughly a quarter of similar patients face a return of disease within three years. Those numbers make the trial’s outcome noteworthy even with its small size.
“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,” said chief investigator Dr. Kai-Keen Shiu, a consultant medical oncologist at UCLH and associate professor at UCL, in the release. The team is cautious but clearly optimistic about what this could mean for select patients.
They also relied on personalized blood testing to follow how people were responding. These tests look for tiny fragments of tumor DNA circulating in the bloodstream, giving clinicians an early read on whether the immune therapy is working before anyone goes to the operating room. “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,” said first author Yanrong Jiang, a clinical PhD student at the UCL Cancer Institute, in the release.
Despite the encouraging signals, the trial has clear limits. It only enrolled 32 people and focused solely on the MMR-deficient or MSI-high subset of bowel cancer, which makes up roughly 10% to 15% of cases. Those constraints mean the results can’t be generalized across all bowel cancer patients just yet. Longer follow-up and larger studies are required to nail down how broadly this approach should be applied.
Still, the researchers see a path toward more tailored care where immune profiling and sensitive blood tests guide treatment intensity. “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,” Shiu said. “These tools could help us tailor our approach, identifying patients who are doing well and may need less therapy before and after surgery.”
