A short course of immunotherapy given before surgery instead of chemotherapy afterward appears to have produced an unusually durable remission in a small group of bowel cancer patients, according to results from the NEOPRISM-CRC trial that have now held up for nearly three years.

All 32 patients enrolled in the study — each diagnosed with stage two or three colorectal cancer carrying a specific genetic signature — remained free of recurrence roughly 33 months after treatment. That includes patients who, after their immunotherapy, still showed tiny traces of residual disease under the microscope.

"After nearly three years of follow-up, none of the patients had experienced a cancer recurrence, including those who still had small traces of disease after treatment."

— Summary of the NEOPRISM-CRC trial results

A different order of operations

Standard care for stage two or three bowel cancer follows a familiar sequence: surgery first, then chemotherapy to mop up any microscopic disease left behind. The NEOPRISM-CRC trial inverted that logic. Patients received pembrolizumab — sold as Keytruda, an anti-PD-1 checkpoint inhibitor — for up to nine weeks before their operation, and the post-surgical chemotherapy was skipped entirely.

The approach reflects a growing conviction among oncologists that the best moment to deploy immunotherapy is while the tumor is still in place. An intact tumor presents the immune system with a full library of targets; once it is removed, that training ground disappears.

Why this genetic subgroup matters

Only a subset of bowel cancers respond to checkpoint inhibitors at all. The trial recruited patients whose tumors are mismatch repair deficient, or dMMR — often described as MSI-high. These cancers carry hundreds of times more mutations than ordinary colorectal tumors, which makes them look conspicuously foreign to the immune system.

That vulnerability is already exploited in advanced disease: pembrolizumab won approval for metastatic dMMR colorectal cancer on the strength of the KEYNOTE-177 trial. What NEOPRISM-CRC suggests is that moving the drug earlier — into the curative setting — may be far more powerful than using it as a last line of defense. dMMR tumors account for only a small fraction of all colorectal cancers, but they are among the most immune-responsive of all solid tumors.

Related laboratory work points to a complementary mechanism. Research summarized under the heading "one gene deletion tears off colon cancer's invisibility cloak" suggests that the loss of a single gene can strip tumors of the molecular camouflage they use to evade immune detection, effectively making them visible to T cells. If that mechanism can be identified and pharmacologically mimicked, it could extend immunotherapy's reach to the far larger population of bowel cancers that are currently mismatch repair proficient and largely unresponsive to checkpoint blockade.

The caveats are substantial

The enthusiasm the result has generated online — where headlines have described tumors "melting away" and remaining absent 33 months later — deserves to be read alongside the trial's limitations.

  • Size: 32 patients is a very small cohort. A single favorable outcome curve in a group this size can be produced by chance, by careful patient selection, or by both.
  • No control arm: Without a randomized comparison against standard surgery-plus-chemotherapy, the trial cannot prove the immunotherapy is responsible for the durability of the remissions.
  • Subgroup only: The findings apply to dMMR/MSI-high disease, a minority of bowel cancers. They say nothing about the typical mismatch repair proficient tumor.
  • Follow-up length: Nearly three years is meaningful for colorectal cancer, but recurrences can still emerge later. Longer surveillance is needed.

Researchers involved in the work have been careful to frame the results as a signal worth pursuing rather than a new standard of care, and definitive answers will depend on larger randomized trials now being planned or underway in the neoadjuvant immunotherapy space.

How the story was told

The different outlets covering the result framed it in markedly different registers. Science Daily emphasized the durability and the vivid imagery of disease that "melted away" and then stayed away, foregrounding the follow-up data. The two syndicated headlines leaned on the arithmetic — "none of 32," "33 months," "kept bowel cancer away in all 32 patients" — compressing the story into a single numeric hook. The medical press, by contrast, chased the biology, asking what makes these tumors visible to the immune system in the first place and whether that invisibility can be stripped away in cancers that currently resist immunotherapy.

Read together, the coverage describes two halves of the same research program: a clinical result that is striking but preliminary, and a mechanistic question whose answer could determine whether the benefit ever extends beyond a narrow genetic subgroup.

What happens next

If the durability holds in randomized testing, the implications for patients would be considerable. Skipping post-operative chemotherapy would spare patients months of nausea, fatigue, neuropathy and infection risk. A nine-week pre-surgical course would also be cheaper and easier to tolerate than a full adjuvant regimen.

For now, the NEOPRISM-CRC data stand as a proof of concept with an unusually clean result: 32 patients, no relapses, nearly three years on. Whether that becomes a template for treating bowel cancer — or an outlier that larger trials fail to reproduce — is the question the next round of studies must answer.