Scientists Report Bowel Cancer Tumors Melted Away After Nine Weeks of Immunotherapy

Christopher Burston’s bowel cancer appeared to disappear after just nine weeks of immunotherapy, yet he still underwent surgery.

The British patient, diagnosed with stage III bowel cancer in 2023, participated in a clinical trial involving 32 patients, with researchers reporting no cancer relapses during nearly three years of follow-up.

The findings, which gained renewed attention in October 2026, suggest a promising approach to treating certain colorectal cancers. But Burston’s experience raises a question: Why operate when treatment appears to have eliminated the cancer?

Researchers at University College London and University College London Hospitals investigated whether immunotherapy before surgery could improve treatment responses. Burston’s experience became a striking example of the drug’s potential, while also revealing why doctors still rely on surgery to assess and manage certain cancers.

Nine Weeks of Treatment Produced a Remarkable Result

Burston received three doses of pembrolizumab before undergoing his planned operation in May 2023.

His experience began in February 2023, when a positive screening result led to further examinations and a diagnosis of stage III bowel cancer.

He subsequently joined the NEOPRISM-CRC clinical trial, which investigated pembrolizumab, an immunotherapy drug that helps the immune system recognize and attack certain cancer cells.

After approximately nine weeks of treatment, Burston underwent surgery. What doctors discovered afterward surprised him.

“The outcome of the surgery was essentially that the cancer had melted away, these were the doctor’s words,” Burston recalled.

The response became central to public interest in the trial, offering an extraordinary example of how effectively immunotherapy can work in some patients.

Why Doctors Still Performed Surgery

The operation was part of the trial’s planned treatment, allowing doctors to examine the affected tissue and determine how completely the cancer had responded.

When no remaining cancer is detected in surgically examined tissue, doctors call the result a pathological complete response.

This finding provides important evidence about how well a medication has worked. However, it does not establish that an operation can safely be skipped, particularly when the trial was designed to include surgery from the beginning.

Researchers investigated the benefits of administering immunotherapy before surgery, not whether the operation could be eliminated.

For Burston, the procedure therefore served both as treatment and as a way to evaluate his response.

Related: 8 Common Health Mistakes Doctors Wish Americans Would Stop Making

What Researchers Discovered in the Wider Trial

The study reported substantial tumor responses among patients with a specific genetic form of colorectal cancer.

NEOPRISM-CRC involved 32 patients with high-risk stage II or stage III colorectal cancer whose tumors had molecular characteristics known as dMMR or MSI-H.

Initial findings presented in June 2024 showed that 17 participants (approximately 53%) achieved a pathological complete response. Among evaluable surgically removed tumors, the rate was approximately 59%.

Updated results presented in April 2026 reported no relapses in the relevant patient group after a median follow-up of 32.9 months.

Dr. Kai-Keen Shiu, the study’s chief investigator, described the results as “extremely encouraging.”

However, the trial was relatively small and did not include a randomized comparison group receiving standard treatment, limiting the conclusions researchers can draw about its effectiveness compared with existing approaches.

What the Findings Mean for American Patients

Pembrolizumab is already approved for certain colorectal cancers in the United States, but the British researchers investigated its use before surgery.

The Food and Drug Administration approved the drug on June 29, 2020, for certain patients with unresectable or metastatic MSI-H or dMMR colorectal cancer.

The NEOPRISM-CRC trial focused on patients with earlier-stage disease who were scheduled for surgery.

According to University College London, approximately 10% to 15% of patients with stage II or III bowel cancer have the genetic characteristics studied.

This distinction matters because the findings cannot automatically be applied to everyone diagnosed with colorectal cancer.

Researchers also examined personalized blood tests that detect circulating tumor DNA. Their findings suggested these tests could help assess treatment responses, although they have not been established as a way to determine whether surgery can be avoided independently.

For Burston, immunotherapy produced a remarkable response, and his cancer remained absent during the reported follow-up period. For researchers, the experience offers another reason to investigate how cancer treatment might become more precisely tailored to individual patients.

How might advances in measuring cancer treatment responses change the way doctors decide when a patient has received enough treatment?

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