A recent study tested a new plan for people with colon cancer. Instead of the usual chemotherapy after surgery, researchers gave a drug called pembrolizumab before the operation.
Strong Results After Three Years
In the trial, 32 patients with stage 2 or stage 3 colon cancer received the drug for about nine weeks before their surgery. After the operation, doctors watched them for almost three years.
Almost all of the patients (59 %) had no sign of cancer after the treatment. And after 33 months, none of them had the disease come back.
Normally, about one‑quarter of similar patients see their cancer return within three years when they get surgery plus chemotherapy. The new approach looks far better.
Blood Tests Can Tell Who Benefits
Scientists also looked at blood samples. They created a simple test that can spot tiny pieces of cancer DNA in the blood. If the test shows no cancer DNA, the patient is very likely to stay cancer‑free.
This test could help doctors know early whether the treatment is working.
Why Colon Cancer Matters
Colon cancer is the fourth most common cancer in the UK, with about 44 000 new cases each year. It mostly affects older adults, but more people under 50 are being diagnosed.
Early detection matters a lot. About 90 % of people with stage 1 disease live at least five years. The number drops to 65 % for stage 3 and only 10 % for stage 4.
Details About the Trial
The study focused on a special type of tumor called MMR‑deficient or MSI‑high, which makes up roughly 10‑15 % of colon cancers in the UK (about 2‑3 000 patients each year).
Instead of the standard route—surgery followed by several months of chemotherapy—these patients got pembrolizumab first. After surgery, they were simply observed.
The results were shared at the 2026 American Association for Cancer Research meeting in San Diego.
How the Drug Works
Researchers found that when cancer DNA disappears from the blood, the chance of staying cancer‑free goes up a lot. They also saw that looking at the tumor’s immune profile before treatment can predict who will respond well.
Real‑World Story
Christopher Burston, a 73‑year‑old from Dorset, was told he had colon cancer after a routine test found blood in his stool. He joined the trial and traveled to London for care.
He received three doses of pembrolizumab over nine weeks, then had surgery in May 2023. The doctors said the tumor had almost completely melted away.
Nearly three years later, Christopher is still cancer‑free and enjoys his daily life.