ctDNA as a Biomarker in CRC


An overview of what is currently understood about the use of ctDNA assays to help guide treatment decisions when managing patients with colorectal cancer undergoing resection of metastases.

Richard Kim, MD: So, another question that comes up is that, how does this paper sort of contribute to our understanding of use of ctDNA as a biomarker for response to a treatment. And this is a more of a prognostic marker at this time and not quite a predictive marker. So, it tells us a prognosis, how well the patient is going to do after surgery. Whether tumor is going to come back or not, I think that's what the circulating tumor DNA is used for. And I personally think this is a better version of CEA. As we know, in clinic we use CEA as a biomarker, it's not a very sensitive biomarker. Sensitivity of CEA is probably 40% at best. It is not a good biomarker, but that's what we typically use. But using ctDNA it is a better version of biomarker where the sensitivity is much higher, maybe 75% to 80%. I think this is how I visioned- how I see the ctDNA at this time. Once again, moving forward, I think this should be incorporated into a clinical study where we make the clinical decision based on the positive tumor DNA and negative, positive- and negative ctDNA. I think that's the future, but right now it is, it seems like it is very prognostic. Understanding that still there are a percentage of patients that tumor will be false negative, or false positive. It is not 100% testing, but however, I think moving forward, hopefully those techniques will get better and we'll have a better technology where we will decrease the chances of having a false positivity or false negativity.

Liliana Bustamante, MD: Absolutely. One thing I think about sometimes, and I'm sure- this comes up on my clinic and I'm sure it comes up a ton in your clinic. Are patients that, for example, have a metastatic disease that have been on treatment for a while and their scans became negative a while ago. There are no evidence of disease on scans for a while, and they're still on chemotherapy week after week, and they're doing well, and- but they're still on chemo. And they're always asking, how long am I going to do this for. And it's very easy for us to say when they have something that we're measuring, that we're following, that's not growing, etc. But when there's no evidence of disease for a while, then it becomes a question about like, am I doing something, am I adding more toxicity or not. And in that setting, again, this is not ready for us to make clinical decisions like that, but when patients decide that they certainly want a chemotherapy break or something like that, that they need it because of toxicities or whatever. Having a negative ctDNA may give at least me a bit of peace of mind, that at least right in that moment there's not a lot of disease or any disease that is detectable. So again, we have to take this with a grain of salt, but in certain scenarios that do come up in clinic, this may be an extra tool to help us.

Transcript edited for clarity.

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