A short course of immunotherapy before surgery left bowel cancer patients relapse-free for nearly three years

A short burst of immunotherapy given before surgery, rather than the usual chemotherapy afterward, has kept a group of bowel cancer patients free of their disease for nearly three years, according to follow-up results from a British trial. The outcome, reported at a major cancer research meeting, drew attention because none of the treated patients had relapsed at the latest check, a marked contrast with what standard treatment would predict.

The NEOPRISM-CRC trial

The study, known as NEOPRISM-CRC and led by University College London and University College London Hospitals, involved 32 patients with stage 2 or 3 bowel cancer. Each of the tumors shared a specific genetic profile described as mismatch-repair deficient, or MSI-high, and every patient received about nine weeks of the immunotherapy drug pembrolizumab before their planned operation instead of the more common sequence of surgery followed by chemotherapy.

Follow-up findings were presented at the 2026 annual meeting of the American Association for Cancer Research. As ecancer reported, the update showed zero relapses among the treated patients well into the follow-up period, a result the researchers described as unusually durable for this stage of disease.

Targeting a specific genetic profile

The trial deliberately selected tumors that are mismatch-repair deficient, a category that accumulates large numbers of genetic mutations. Those mutations make the cancer highly visible to the immune system, which is why this subtype tends to respond unusually well to checkpoint immunotherapy. Pembrolizumab works by releasing a brake on immune cells called T cells, freeing them to recognize and attack the tumor.

Only a portion of bowel cancers carry this profile, so the approach is not a universal treatment. But for the patients who qualify, the biology appears to create an opening that immunotherapy can exploit before an operation ever takes place, and identifying that subgroup in advance is what made the trial possible.

What the follow-up showed

Initial results indicated that 59 percent of patients had no detectable signs of cancer after the pre-surgery immunotherapy and their operation. The more striking figure came later: at roughly 33 months of follow-up, none of the 32 patients had experienced a return of the disease, including both those who were cancer-free after treatment and those who had small amounts of residual disease that did not grow or spread, according to UCL.

For comparison, under standard care roughly a quarter of patients treated with surgery followed by chemotherapy are expected to relapse within three years, which is what made the absence of any relapses in the trial notable to the researchers. The gap between that expectation and the observed result is the reason the follow-up attracted attention.

Why pre-surgery timing may matter

Giving immunotherapy while the tumor is still in place may allow the immune system to mount a broader and more durable response than it could after the cancer is removed, since the intact tumor provides a rich set of targets for T cells to learn. Several patients also avoided the extended chemotherapy that would normally follow surgery, sparing them additional toxicity and a lengthy recovery.

The result adds to growing interest in using immunotherapy earlier in the treatment sequence for the subset of cancers most likely to respond, rather than reserving it for advanced disease once other options have been exhausted. That earlier timing, known as neoadjuvant treatment, is being explored across several cancer types.

The approach also fits a wider rethinking of how bowel cancer is treated. For tumors with the mismatch-repair-deficient profile, standard chemotherapy has long been recognized as less effective than in other colorectal cancers, which sharpened the rationale for testing an immune-based strategy in exactly this group. The trial, in effect, matched a treatment to the biology most likely to respond to it, rather than applying a one-size-fits-all regimen.

Limits and next steps

The trial is small, with only 32 participants, and it tested a single approach in one narrow genetic subtype without a randomized comparison group. Researchers caution that longer follow-up and larger studies are needed before pre-surgery immunotherapy could become a standard option, even for eligible patients. The findings are best read as an encouraging early signal that will require confirmation, not a settled change in practice.

Even so, for a disease in which relapse after surgery remains a persistent threat, a treatment that left every patient in a trial disease-free for nearly three years represents a result oncologists say is worth pursuing in the larger studies that would be needed to confirm it.

If those larger studies bear out the pattern, the practical appeal is considerable. A nine-week course of immunotherapy that allows some patients to avoid both extensive surgery and months of chemotherapy would represent a lighter treatment burden as well as a more effective one, an unusual combination in cancer care. For now, the researchers frame the result as a foundation for that larger work rather than a finished case for changing how bowel cancer is treated.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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