This week, Bobbi Conner talks with Dr. Maggie Westfal about a blood test being used to detect the return of colon cancer. Dr. Westfal is an Assistant Professor of Colorectal Surgery and a colorectal surgeon at MUSC Hollings Cancer Center.
TRANSCRIPT:
Conner: I'm Bobbi Conner for South Carolina Public Radio with Health Focus here at the radio studio for the Medical University of South Carolina in Charleston. A blood test that looks for tiny fragments of tumor DNA in the bloodstream is now being used to detect the return of colorectal cancer after treatment is completed. Doctor Maggie Westfal is here to talk about the details. Doctor Westfal is an Assistant Professor of Colorectal Surgery, and she's a colorectal surgeon at MUSC Hollings Cancer Center. Doctor Westfal, tell us about the circulating tumor DNA blood test that has become an important tool to help detect the return of colon cancer.
Dr. Westfal: The circulating tumor DNA is a new test that's come out in the last five years, to look at tiny pieces of DNA fragments from your specific tumor that circulate in your blood. We usually do the test at diagnosis and then use it for surveillance after treatment.
Conner: How effective is this blood test, then, at detecting the return of colon cancer.
Dr. Westfal: From a colorectal cancer specific perspective, the sensitivity of the test is about 70 to 80%, so 70 to 80% of the time when it's positive, it's detecting cancer DNA that's circulating in your bloodstream. It has a specificity of about 90%. So, if it's negative, 90% of the time it's truly negative.
Conner: I understand that this test is especially effective at early detection of the return of colorectal cancer compared with some other types of cancer. Why is this the case?
Dr. Westfal: So, colorectal cancer is known to have shed its DNA more often than other cancers. And so, they're able to use the ctDNA as a surveillance marker for that reason.
Conner: When is this blood test typically being used then for colon cancer survivors?
Dr. Westfal: ctDNA is being used in our surveillance guidelines. And so, all of our patients will get a ctDNA, as I said at diagnosis. So, it uses the biopsy of your tumor to create the tests that we then use for surveillance. That test is run every three months for two years, and then every six months for an additional three years, for five years of surveillance.
Conner: If this blood test is positive for tumor DNA in the bloodstream for an individual patient, then how does this help guide treatment moving forward for that patient.
Dr. Westfal: Yeah, I think that's kind of one of the main key points about ctDNA is it allows for a more individualized approach to cancer surveillance for each of our patients. A positive test in, let's say, for example, a very frail patient may indicate that we need to consider treating with chemotherapy or immunotherapy in a patient that we may not have, had their ctDNA been negative, due to their frailty. So, a patient that comes to us after having surgery, for instance, and let's say at the six month mark, their ctDNA then becomes positive. That might be someone that we get new imaging at that moment, instead of at the year mark, which is when we usually get our imaging post-op. And so, I think in two ways, it allows us to make individualized approach about treatment after surgery. And then it allows us to identify patients that may be recurring earlier than we would expect them to.
Conner: Doctor Westfall, thanks for talking with us about using this blood test to detect the return of colorectal cancer.
Dr. Westfal: You're welcome. Thanks so much for having me, Bobbi.
Conner: From the radio studio for the Medical University of South Carolina in Charleston, I'm Bobbi Conner for South Carolina Public Radio.
Health Focus transcripts are intended to accurately represent the original audio version of the program; however, some discrepancies or inaccuracies may exist. The audio format serves as the official record of Health Focus programming.
