Bowel cancer is one of those diseases most of us have brushed up against, through a parent, a sibling or an older friend. For many patients, the treatment path has looked the same for years. Surgery, then months of chemotherapy.
In the NEOPRISM-CRC trial, led by researchers at University College London, 32 patients with stage 2 or 3 bowel cancer were given up to nine weeks of the immunotherapy drug pembrolizumab before surgery. The short course replaced the usual post-operative chemotherapy.
After an average of 33 months of follow-up, not a single patient had relapsed. The results were reported at the AACR Annual Meeting 2026. By comparison, around a quarter of patients given standard surgery plus chemotherapy relapse within three years, according to the UCL team.
Why this only works for one bowel cancer subtype
The trial enrolled only patients with MMR-deficient bowel cancer, sometimes called MSI-high. In these tumors, the cells have lost their system for fixing small DNA errors, so they build up a very large number of mutations.
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That genetic clutter is what the immune system can learn to attack. It is one reason immunotherapy works far better here than in most bowel cancers.
This profile shows up in only 10 to 15 percent of stage 2 and 3 bowel cancers, so the finding does not change care for the majority of patients today.
Among the 32 trial patients, 59 percent had no detectable cancer left after the pembrolizumab course and the planned surgery. The rest still had small amounts of disease, but those traces did not grow or spread during the follow-up window.
What this means for patients now
Pembrolizumab is already approved for several cancers under the brand name Keytruda, made by Merck. What is new here is using it before surgery, as a short course that replaces chemotherapy entirely.
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This is still a Phase 2 study with only 32 patients, so a larger trial will be needed before it becomes a standard option. The team is also developing personalized blood tests to pick out, in advance, who is most likely to respond.
Chief investigator Dr. Kai-Keen Shiu, from the UCL Cancer Institute, said the three-year outcomes strengthen the team's confidence in the approach. He called pembrolizumab a safe and effective treatment for high-risk bowel cancers in this subgroup.
In the United States, colorectal cancer is the second most common cause of cancer death when men and women are combined, according to the American Cancer Society. The ACS projects about 55,230 deaths from the disease in 2026.
MMR status is typically checked on the tumor biopsy, so patients recently diagnosed with bowel cancer can ask their oncologist whether their tumor falls into this subtype.
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This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.