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Released: July 29, 2026

John Marshall
John Marshall, MD
Catch Up On All Episodes of Oncology Unscripted

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When Dogs Detect Cancer

[00:00:06] John Marshall, MD: John Marshall, Oncology Unscripted. Happy summer. It is a hot summer here in Washington. We did have that thunderstorm last night—some tornadoes not too far away—but we made it. We needed the water. I hope nobody got hurt. I don't think so. I've been thinking a little bit lately about, as we get older, what the proper dress is to go to work in, and I'm still a guy that kind of wears a tie every now and then. I wear a tie on patient days, particularly. During the pandemic, if you're like me, a lot of people stopped wearing ties. That whole infectious disease thing about ties—if I'm wearing a white coat anyway, I'm not really sure about it. I was just in a meeting, a global sort of drug development meeting, and there were only two other men wearing ties in the meeting. And I kind of brought it up, and they all were razzing each other. The younger ones without ties were razzing the older ones with ties. And then I'm not even sure this tie actually works with this shirt, but you know what? What the heck, at my age and on Oncology Unscripted, I can pretty much wear what I want.

So, welcome to our July episode of Oncology Unscripted.

A lot has been going on since ASCO, but I wanna drill down on our main topic, as it is something that really is starting to shift how we're thinking about screening for cancer. Now, you all know, and I know, that there are only a few cancers that we typically screen for, right? They are breast and colon, and now lung if you're a smoker, as well as skin cancers and cervical cancer.

But what screening was supposed to be was inexpensive and noninvasive, with high sensitivity and high specificity.

But as you know, there's been an increasing shift and emphasis on screening for cancers in general. And so, the latest one that just came out is actually pretty controversial because we've been talking a lot about precision medicine and being able to find tumor/cancer DNA in the blood.

We've been doing this as a predictor of recurrence in patients with known cancer. But as you also know, there has been increasing work in patients who are well, who are just going in to be seen by a doctor and get a checkup, and who are getting blood tests using blood screens for cancer. And very recently, there was an approval for a blood test looking for colon cancer.

And when this came out, the American Cancer Society actually put out a position that said, “We support this.” You have to be very careful with the language because what happened on the news that night was that they said, “Blood testing is now approved for screening for colon cancer.” That's not really what it says.

What it says is, if the patient refuses a colonoscopy, if the patient refuses stool testing, then you can default to blood testing. And remember, colonoscopies are designed around the biology of polyps, so you only need to do them every so often, okay, whereas stool tests and blood tests need to be done much more regularly. And I don't think that message gets out to people at all.

One-and-done is not really what you need for blood testing or stool testing. And so, it really sent a very mixed message that we in the colon cancer community were a bit uncomfortable with.

But it's gonna go even further because now all of those cancers that we're not screening for automatically—you could go in, in theory, and get tested to see whether you have bile duct cancer or pancreas cancer or some other cancer that's out there.

And so, we're clearly going to see an increasing trend of this. We're clearly seeing that those companies that do blood testing for cancer patients are gonna move to the earlier screening, uh, place. And maybe, just maybe, one day we'll do blood tests—oh, you have cancer—and we'll treat it without having to do scans and surgery. Fingers crossed that that's where it evolves.

But then, with all of this background, my favorite article of the month is in this journal called The Journal of Clinical Oncology. You remember that. This is a paper journal. And it caught my eye immediately 'cause it starts off with canine olfaction. Now, I don't know if you're a dog lover or not; if you're a cat person, maybe you have fish.

I'm a dog person, and this says, “Canine olfaction combined with Bayesian modeling,” my favorite kind of statistics, Bayesian modeling, “for multicancer detection from breath samples.” It's a phase 2 study done in India, where they don't have the resources to be doing blood testing on people. And this paper makes it into the Journal of Clinical Oncology because, guess what?

The dogs were able to do it. They got breath samples; they were trained first; they got breath samples; and, with pretty high statistical positivity and sensitivity, they were able to find patients who had early cancers and those who did not. And so, all I could think about is: how much money are we spending on going to get this blood test when, in fact, maybe, you know, your daughter's dog—that's my favorite grand-dog.

I don't have any grandchildren; I have a grand-dog. But maybe it's your daughter's dog that's gonna come up and go, “You know what? Maybe you should get checked because I'm a little worried about you.” But I just loved this paper, and I commend it to you.

But I do think we, as the medical community, need to be responsible overseers of this message: yes, this blood test is out there; yes, it is for patients who refuse any other test because some test is probably better than no test.

But you can't rely on a negative to say, “Oh, it was negative; I don't have cancer,” like you can with some of these other, more traditional tests. So, just keep a nose out for the latest news in precision medicine and its use for screening; maybe one day we won't do all these blood tests, and we'll just let our pups do the sniffing.

John Marshall, Oncology Unscripted.

This transcript was generated by AI and lightly edited.