Right now, as we speak, there exists a relatively inexpensive method for detecting certain early

cancers with an accuracy rate of up to ninety-seven percent.

You might even have one in your room with you right now home.

And it probably goes wild when you reach for a tennis ball or the doorbell rings.

Yes -- we're talking about the domestic dog.

So why aren't there domestic dogs trained to detect cancer in every hospital on the

planet?

It's complicated.

Anecdotally, there are a lot of stories out there about dogs who seemed to smell lung

cancer on their owner's breath, or became unusually interested in a particular mole

later found to be cancerous.

But there's also more rigorous evidence too.

In fact, a 2019 study found that some dogs can detect lung cancer in blood samples with

almost 97% accuracy.

And that's not too surprising when you consider that dogs can learn a huge amount about other

dog's health, age, and reproductive status by smelling their butts.

But how they're able to separate the smell of healthy cells from cancerous cells is pretty

remarkable.

Cancer cells produce odiferous chemicals called volatile organic compounds, or VOCs. And dogs

sometimes actually detect a particular cancer's signature blend.

The particular group of VOCs produced by a given type of cancer can act as a biomarker

for that cancer.

A biomarker is any biological characteristic that can be measured and then used to identify

some sort of process in the body.

If that sounds vague, it's because biomarkers can be a huge range of things. But in this

case, they make it possible to tell healthy tissue from cancerous cells.

VOCs are produced during normal biological processes. They might be present in skin,

urine, blood, sweat, stool, or even a person's breath, where they can serve as biomarkers

for both healthy and diseased biological processes.

That's because the VOC profile you see in these places is different in people with,

say, lung cancer, than it is for healthy people.

And it's different in people with lung cancer than it is in people with ovarian cancer,

or bladder cancer, or breast cancer.

Detecting cancer-specific VOCs is complicated for us humans because there are so many to

sort through — there can be as many as 3000 different VOCs in a person's healthy exhaled

breath.

In 2003, researchers were able to identify two classes of VOCs — alkanes and monomethylated

alkanes — as possible tumor markers in lung cancer patients.

The specific biomarkers of many other cancers haven't been identified yet.

That's mostly because it's challenging to pick out the few VOCs that are specific

to a given cancer from all the other given compounds that might be present in a sample.

But if that two 2019 study is any indication, some of our fine furry friends can be trained

to sniff them out.

So you'd think every hospital and doctor's office and diagnostic lab that doesn't already

have a cancer-sniffing dog would be trying to get one. But there are some technical barriers,

despite these pooches' impressive accuracy.

Dogs thrive in jobs that require a close relationship with a handler.

Dogs that sniff out drugs or bombs, or who look for survivors of disasters, work in a

very engaging environment.

These jobs are exciting for dogs. The animals are working in an environment with a lot of

external stimuli, and that moment where a survivor is found under a pile of rubble can

be, like, emotional for everyone involved.

And a search and rescue dog's handlers can confirm that the dog has found its target,

which means the dog will always get the right reinforcement at the right time.

Compare that to a bunch of dogs in a lab sniffing out sample after sample, most of which probably

won't be positive.

That could be frustrating for a dog.

But the biggest problem in that real-life scenario is that the handlers can't give

the dogs any feedback if they don't know which samples are cancerous.

If they reward the dog for every alert, they could unknowingly be rewarding false positives,

which will ultimately impact the dog's accuracy.

No rewarding means no joy, and those cancer-sniffing canines could easily start regretting their

career choice.

And even though the dogs can be pretty accurate in theory, things could be different in practice..

Like people, dogs are fallible.

I don't wanna… don't send me hate mail!

And unlike a hypothetical cancer-sniffing machine, a dog might work better in the morning

and not so great in the afternoon, which would result in different rates of accuracy.

You don't have that kind of problem with a machine, which operates the same way every

time you use it.

Finally, it's a huge investment of both time and money to train a cancer-sniffing

dog.

A single dog needs to spend six to eight months sniffing a minimum of 300 biological samples

before they can be a certified cancer-sniffer.

But that doesn't mean we can't learn a lot from cancer-sniffing canines.

Dogs can still help us identify the odor signatures of different cancers.

We could use that information to build electronic noses -- a robot cancer-sniffing dog.

Like, not literally, but it was fun to say....

These devices are already being tested, but more work needs to be done to determine which

VOCs the noses should be looking for, as well as to improve their overall accuracy.

So far, some studies are using electronic noses to look at patterns of VOCs, rather

than picking out specific ones, because the specific VOCs aren't always known.

And electronic noses still aren't as accurate as some dogs are.

Other medical conditions, for example, can sometimes interfere with the machine's ability

to spot cancer.

One study on using VOCs to detect bladder cancer found that the presence of an infection

could reduce the accuracy of the electronic nose. Which means there's more progress

to be made.

Still, while it's fun to imagine legions of lab coat-wearing canines quietly saving

lives behind the scenes, it's probably not going to happen in quite that way.

But the things we've learned from dogs and their amazing olfactory abilities are already

helping us build technologies that will save lives through early diagnosis.

So break out the tennis ball, and thank your best friend for their help.

Thanks for watching this episode of SciShow. If you like what we do here, you can support

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