ctDNA Assays in CRC: Interpreting Clinical Findings

Following presentation of a paper by Loupakis F, et al., Drs Liliana Bustamante and Richard Kim raise questions pertaining to the use of ctDNA as a biomarker when managing patients with metastatic colorectal cancer undergoing resection.

Richard Kim, MD: You know, this paper gives us a lot of insight in the role of using circulating tumor DNA in the setting of resectable metastatic colorectal cancer. However, it does raise a lot of question, that we don't have an answer to. I think one of the questions that came up was that once again, this trial didn't control what kind of chemo patient got before or after. There were some patients got chemo before and never got chemo afterwards, or vice versa. Some patient got surgery first, then get chemo afterwards. But I think the main, the clinical question that sort of bring- that this paper does bring up, is that in patients let's say, get chemo for six months prior to surgery. Let's say FOLFOX for six months prior to a surgery and they go under surgery, and if a tumor DNA is positive afterwards, what do you do in those patients. Do you start FOLFIRI in those patients or do you watch them until there's radiographic evidence of recurrence. I think those are the questions that we don't have answer to, because clearly if you have a positive circulating tumor DNA, most likely that tumor will come back. Obviously, the lag time, it will be months, but it will eventually come back. The question is, should you start chemo right away, or should you wait until there is a radiographic finding. I think that's the dilemma that I think a lot of clinicians will face when we start using this circulating tumor DNA. Any thoughts Dr. Bustamante?

Liliana Bustamante, MD: I agree. I agree completely with that. That's probably the biggest question that this paper is raising, especially because adding those therapies doesn't come with its own bag of side effects. Are we doing anything for their overall survival or prognosis by adding them earlier before progression? If progression never comes, when do we stop. So absolutely it’s things that will need to be investigated going forward and I think that's going to be the biggest issue with interpreting this test in the clinic.

Transcript edited for clarity.

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