A blood test could save some colon cancer patients from getting unnecessary chemotherapy following surgery, while making sure that those who would benefit from the treatment get it, researchers report.
The circulating tumor DNA (ctDNA) test looks for minute amounts of genetic material that are released by cancerous tumors, explained co-researcher Dr. Anne Marie Lennon, director of gastroenterology and hepatology at the Johns Hopkins University School of Medicine, in Baltimore.
The presence of cancer DNA in the blood is a sign that someone likely needs follow-up chemotherapy, Lennon said.
The test nearly halved the number of people with stage 2 colon cancer who got follow-up chemotherapy after surgery – 15% versus 28% for a control group that received standard cancer care, the researchers found.
At the same time, both groups had essentially the same chance of two-year recurrence-free survival, 93% for the blood test group and 92% for the group that got regular care.
"Its bottom line was no difference. This is the first study of its kind to use ctDNA to guide patient therapy," Lennon said. "This is the first study that has shown you can use circulating tumor DNA to really personalize cancer care."
About 151,000 new colon cancer cases are expected to be diagnosed in the United States in 2022, according to the American Society of Clinical Oncology. An estimated 52,580 deaths will follow.
For this clinical trial, researchers recruited 455 patients with operable stage 2 colon cancer in Australia and New Zealand. At stage 2, colon cancer has gone through the lining of the bowel but hasn't spread into the lymph nodes, Lennon said.
It's known that about 80% of stage 2 colon cancer patients will be cured solely by surgical removal of their tumor, while 20% will have the cancer come back unless they get follow-up chemo, Lennon said.
In the study, two-thirds of patients were randomly assigned to get the ctDNA blood test about four weeks after undergoing surgery. The rest had their need for follow-up chemo assessed in the current manner, by making a judgment call after looking over the removed cancer and assessing how it had spread in the colon.
Patients with a positive ctDNA result who underwent post-surgery chemotherapy wound up with a three-year recurrence-free survival rate of 86%, according to the investigators.
The researchers presented this study on Saturday at the annual meeting of the American Society of Clinical Oncology (ASCO), held in Chicago. The results of the clinical trial were also published in the New England Journal of Medicine.
This study likely will change the way that stage 2 colon cancer is treated, said ASCO Chief Medical Officer Dr. Julie Gralow.
"If I were a patient, I would want to know what my ctDNA showed, for sure," Gralow said. "And I do think this is really pretty solid data, so I think that it has a high likelihood of impacting standard of care in the U.S."
The test would spare many people from the debilitating effects of chemo, including nausea, vomiting, fatigue and potential nerve damage, Lennon noted.
At the same time, it would increase the chance that high-risk people get chemo even if doctors would be otherwise hesitant to have them undergo it.
"Often there's a hesitancy to give older people chemotherapy," Lennon said. "We're going to be able to say, look, if you're ctDNA positive, we know your risk of recurrence is very high. Even if you are older, you should take the chemotherapy."
Gralow and Lennon added that this is a process that could be put into place immediately for colon cancer patients anywhere in the United States.
While only major cancer centers could perform such a blood test in-house, there are specialized labs to which the blood could be sent for the same analysis, the researchers added.
"They do high volume and do it extremely well, and the cost of it has come down dramatically," Lennon said. "It's something that everybody should be able to have access to."
The next steps will be to take the ctDNA test and see if it can be applied to later stages of colon cancer, as well as other types of cancer, to help judge who might benefit from chemotherapy, Lennon said.