Can dogs detect lung cancer?

Waikato University psychology researcher Dr Tim Edwards is leading a team training pet dogs - including his own, Tui - to try to do just that.

There was a big need for a cheaper and less intrusive way of mass screening for lung cancer, as referrals for testing often came too late, he said.

"The disease has a high mortality rate, so being able to make even a small difference would help save lives."

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Largely due to that reason lung cancer remained our biggest cause of cancer death, often spreading to other parts of the body by the time it was diagnosed.

Typical early symptoms included a persistent, worsening cough, coughing up excessive phlegm with blood, chest pain with coughing or breathing or recurring chest infections.

But if Edwards' study succeeded, a dog might be able to sniff out cancer from a simple breath or saliva sample.

His project, backed by new grant from the Waikato Medical Research Foundation, was using the only known fully automated scent detection mechanism for dogs.

The animals put their muzzle in the device, breaking a beam of light as they sniff the sample.

If the dog held its nose inside for a set period, it was considered a positive indication - and the dog was rewarded with a food treat.

It wasn't the first time the approach had been used to try to detect cancer, and some studies appear to show promise.

One German study published in 2011 found how trained dogs were able to identify cancer in 71 of 100 samples from patients, and were also able to rule out 372 of 400 samples known not to have cancer.

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Other studies have shown canines, which hold 25 times more smell receptors than humans, appear to also have promising potential to detect colon, bladder and skin cancer.

But the scientific case remained far from clear - and research groups have been able to substantiate results so far.

Many researchers have also met the idea with much scepticism.

Commenting in the blog Science-Based Medicine on one other study where dogs had been trained to detect lung and breast cancers, US physician Peter Lipson wrote: "The methodology of breath sampling is not validated as far as I can see, and once again, the putative compounds in breath are not identified.

"Statistically, the efficacy is marginal at best."

Edwards said one of the first things people asked him was what are the dogs were actually smelling.

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"If we could answer that question and list a few chemicals or something, that would make people happier about the science," he said.

"In one sense, we are all curious about that, but in another it doesn't matter.

"They're probably actually smelling a whole bouquet of compounds, and each dog's definition is likely to be a bit different."

Edwards, a specialist in animal behaviour, was using a range of pet dogs.

"It's not about the breed, as all dogs have ridiculously sensitive olfaction," he said.

"It's about their temperament and willingness to work."

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There's currently work being done on e-noses and electronic detection, and Edwards believed that, one day, people may be able to breathe into a machine and have diseases diagnosed.

But that still wasn't close to reality at the moment.

"Right now we do have dogs, and they have some potential according to existing research - but we need to clarify how accurate and reliable they can be."