Dogs can sniff out cancer, adding a new dimension to the image of man's best friend, according to research published today. Doctors writing in the British Medical Journal (BMJ) have presented the first scientific evidence of the canine's ability to put its exceptional sense of smell to good use in detecting tumours.

Tumours are thought to produce volatile organic compounds with a distinctive odour, but often in quantities too small for humans to detect.

For years, doctors have discussed anecdotes about patients who turned up in the surgery worried about a skin blemish or a mole after their pet dog kept licking or nuzzling it, which turned out to be cancer.

Now research has indicated that the canine sense of smell, said to be 1,000 times better than the human one, can indeed pick out malignancies.

Researchers from Amersham Hospital in Buckinghamshire, working with dog handlers from a charity for the deaf, trained six dogs of varying breeds and ages to spot the distinctive odour of malignant cells. After seven months, the dogs were able to identify cancer in samples three times more often than would be expected by chance.

They were given urine samples to sniff from 36 patients with bladder cancer, which they had to distinguish from 108 control samples from patients with other non-cancerous bladder problems and from healthy individuals.

For the final test, the dogs were given seven samples, from which they had to select the one with bladder cancer. They did so by lying down next to it.

The results showed that the dogs chose the right sample on 22 out of 54 occasions, a success rate of 41 per cent, compared with 14 per cent expected by chance alone. "Our study provides the first piece of experimental evidence to show that dogs can detect cancer by olfactory means more successfully than by chance alone. The results we achieved should provide a benchmark against which future studies can be compared," the doctors wrote.

John Church, a retired orthopaedic surgeon who led the study, first encountered the diagnostic skills of dogs in the case of a 66-year-old man who developed a patch of eczema on his leg. The man's pet labrador, called Parker, began to push his nose persistently against his owner's trouser leg. The patch of eczema turned out to be a skin cancer, and once it was removed the dog's behaviour stopped.

After Mr Church described the case in a letter to The Lancet published in 2001, other patients contacted him with similar stories.

He said yesterday: "I have collected 16 cases now. One involved a lady with a chihuahua who would sit with it resting on her bosom as she watched television. It turned round and started nuzzling and pushing against her breast. She went for a mammogram and they found breast cancer."

He added: "We can't say the dogs recognise cancer. But we know that dogs are good at recognising danger that threatens their owners. That is what they are sensing."

In another case, a dog belonging to a deaf person had been taken to visit its owner while she was in hospital. Shortly after arriving on the ward it started barking and was obviously agitated by the patient in the neighbouring bed. The patient had had a cardiac arrest and, thanks to the intervention of the dog, was resuscitated.

Mr Church said he had been "trying for years" to set up a research project to test his canine theory but had not had success until now. "I have been extremely fortunate to discover a dog-training team close to my home," he said.

The trainers, from the charity Hearing Dogs, which supplies dogs for the deaf, used their own pets in the project. The results showed that the three cocker spaniels performed best, closely followed by the papillon, and the mongrel did worst.

Future research would focus on improving the accuracy of the dogs and extending their detective skill to other cancers, Mr Church said.

In a commentary on the findings, also published in the BMJ, Professor Tim Cole of the Institute of Child Health said the findings were striking and novel. One of the most surprising was that the dogs consistently identified one of the control patients in the study as a cancer case. When doctors tested the patient again he was found to have kidney cancer.


Gillian Lacey was 19 when the family's pet Dalmatian began paying close attention to a mole on her leg. "She came and licked and sniffed at it. At first I thought I must have splashed something on my leg and pushed her away," she said. "But she kept coming back to it and I wondered what was wrong."

It was 1978 and she had recently read the Richard Adams novel, Plague Dogs . "He talks about the dogs going past the cancer laboratory and showing evidence that they could smell it. That made me think." But she did not do anything immediately because the mole was so tiny and she couldn't think what she would tell her GP.Her dog, Trudii, would not give up and eventually Ms Lacey asked a friend, whose father was a doctor, for advice. He told her to seek help without delay. A biopsy showed a malignant melanoma and the mole was removed. "I was shocked. I think I had been confident that my dog knew something was wrong but at the same time I hadn't wanted to believe it. I think I was lucky it was detected so early."

Ms Lacey, of Princes Risborough, Buckinghamshire, remains healthy and is a founder member of the charity, Hearing Dogs, that provided the dogs for the cancer detection project.