Whose Test Is It Anyway?
The patient-choice argument behind circulating tumor DNA (ctDNA), the trial that just changed what "clinical utility" means, and what to bring to your next appointment.
There’s a debate within oncology regarding the actionability of ctDNA tests.
Some oncologists believe the average cancer patient can’t handle ambiguous information. They believe that when faced with a test result that says something is here but we’re not sure what it means or what to do about it, most patients will spiral. They’ll demand action when no action is warranted. They’ll lose sleep, lose function, lose perspective. The kind thing, the protective thing, is to not order the test in the first place.
I understand the impulse. Amy L. Delson, AIA, this week’s guest on Kicking Cancer’s Ass, knows it better than most. She’s been treated for cancer four times, and she’s in active treatment right now.
But there is a gap in the argument, and Amy was the one who showed me where. She’d interviewed a fellow breast cancer advocate who told her: we want to know everything we can know. We have young children at home, we have our jobs, but you have to really explain it to us in a way we can understand. And then let us decide.
Your Blood Shows Cancer Is Back 8 Months Before a Scan Does (Episode #45): Apple | Spotify | YouTube | Everywhere
Each patient has their own perspective; the patient is the one who knows what trade-offs she’s willing to make.
What ctDNA actually is, in plain terms
Circulating tumor DNA is exactly what it sounds like. Cancer cells release (shed) fragments of ctDNA into the blood stream. That DNA can be detected through a blood draw and matched against either a tumor sample or a panel of known cancer mutations. If the test finds tumor DNA in your blood, it is called “ctDNA positive.” If it doesn’t, it is called undectable ctDNA or “ctDNA negative.”
What is known is that persistent ctDNA positivity is prognostic for a poor outcome. However, personalized therapy interventions may improve outcomes, assuming we know what therapy to use. We know that persistent ctDNA+ is not good - but we don’t know what to do about it, yet. Tests market right now include Signatera, Oncodetect, Personalis, Guardant, and FoundationOne, with new entrants arriving regularly. At the cancer genomics conference at the University of Chicago in April 2026, I saw the next wave coming.
