A blood test under study may soon be able to help many patients with colon cancer decide whether they need chemotherapy after surgery, or if they can safely skip it.
The results, which oncologists described as promising, were published in the journal Nature Medicine.
Currently, many patients with surgically removable colon cancer are automatically given additional chemotherapy, but doctors can't perfectly predict who will or will not benefit from this. Although the blood test may need to be studied further before it becomes part of standard medical care, oncologists see it as a promising tool that could help many patients safely skip chemotherapy -- and its harsh side effects.
"Potentially, worldwide, we're talking about millions of people," said Dr. Alok Khorana, director of the gastrointestinal malignancies program at the Cleveland Clinic, who was not involved with the study. "Colorectal cancer is one of the most common cancers in the country, affecting both men and women. Worldwide, it's also very common and is rising in many countries where in the past, it was not that common."
The blood test, made by genetic testing and diagnostic company Natera, is also sometimes called a "liquid biopsy." It detects small fragments of genetic material called circulating tumor DNA (or ctDNA), which are shed by the cancer into the blood stream.
In the recently published study, researchers looked for the presence of this genetic material in more than 1,000 patients who had undergone surgery to remove stage II, III, and IV colon cancer. A positive test suggests there are still residual cancer cells in the body. This study showed that patients with positive tests likely need additional chemotherapy, whereas those with negative tests might be able to safely skip the taxing and toxic treatment.
"What the study showed was that the people who had the liquid biopsy, or ctDNA, being positive after surgery, had an extremely, extremely high chance of recurrence...10 times higher risk compared to people who were ctDNA negative," said Dr. Suneel Kamath, a gastrointestinal oncologist at the Cleveland Clinic, who was also not involved with the study. "What's interesting too was that was by far the strongest factor. We use a lot of other factors, like how progressive the tumor is and how many lymph nodes are involved."
Currently, oncologists use other clues -- such as the characteristics of the tumor itself -- to help them gauge which patients need additional chemotherapy. But this new study suggests the blood test would be more accurate, Kamath said.
"Even though we've been relying on those for many decades, all of those were far, far less predictive of who was going to have their cancer return," Kamath said.
Still, experts said, more research is needed before this test becomes a standard part of medical care.
"The impact of this individual paper should be taken into the context of other papers that have recently come out and are ongoing...It has a meaningful impact in allowing us to not only identify high-risk patients, but also showing that giving them chemotherapy after the surgery is beneficial," said Khorana.
A June 2022 trial published in the New England Journal of Medicine also showed that ctDNA can be safely used to guide chemotherapy decisions in stage II colon cancer. This study shows that there is also benefit for stage III and stage IV cancers.
And more research studies are ongoing.
"The findings of this study are provocative, but not sufficient to just yet change clinical practice," Khorana said, "although I foresee that that's going to happen very, very soon in the near future."
He added, "I would encourage patients to join those trials because that is the best way to find out...whether drugs work or not, and whether tests work or not."
Jason Nasser, MD is a resident physician in Internal Medicine from Cleveland Clinic in Ohio and a member of the ABC News Medical Unit.