News in Science

Dogs sniff out cancer in stool

Clever canine Japanese researchers are reporting a 'lab' breakthrough: a retriever that can detect bowel cancer in breath and stool samples as accurately as hi-tech diagnostic tools.

The findings, presented today in the Gut , a British Medical Journal publication, support hopes for an 'electronic nose' that could one day sniff a tumour at its earliest stages, the researchers say.

The team, led by Hideto Sonoda at Kyushu University in Fukuoka, Japan, used a specially-trained female black labrador to carry out 74 "sniff tests" over a period of several months.

Each of the tests comprised five breath or stool samples, only one of which was cancerous.

The samples came from 48 people with confirmed bowel cancer at various stages of the disease and 258 volunteers with no bowel cancer or who had had cancer in the past.

Incredibly high accuracy

They complicated the task for the eight-year-old canine detective by adding a few challenges to the samples, including samples from smokers or from subjects with other types of gut problems, which might have masked or interfered with other smells, but these did not interfere with the dog's olfactory accuracy.

Around half of the non-cancer samples came from people with bowel polyps, which are benign but are also a possible precursor of bowel cancer.

Six per cent of the breath samples, and 10 per cent of the stool samples, came from people with other gut problems, such as inflammatory bowel disease, ulcers, diverticulitis, and appendicitis.

In the study, the retriever performed as well as a colonoscopy, a technique in which a fibre-optic tube with a camera on the end is inserted into the rectum to look for suspect areas of the intestine.

It correctly spotted which samples were cancerous and which were not in 33 out of 36 breath tests, equal to 95 per cent accuracy, and in 37 out of 38 stool tests (98 per cent accuracy).

It performed especially well among people with early stage disease.

The researchers say that this study shows that cancer cells give off specific discernible odours as they circulate through the body.

Previous research has also found that dogs can sniff out bladder, lung, ovarian and breast cancer.

The authors concede that using dogs as a screening tool is likely to be impractical and expensive, but that a sensor could be developed to detect specific compounds that are linked to cancer, in faecal material or the air.

Early detection is the 'holy grail' in bowel cancer fight

Dr Trevor Lockett, theme leader on colorectal cancer and gut health in the CSIRO Preventative Health National Research Flagship, said he thinks the Japanese team's findings are fascinating.

"Most striking is the ability of the dogs to detect bowel cancer at its earliest stages," he says.

He says that most current non-invasive tests for bowel cancer are far better at finding later stage disease than early stage.

"Detection of early stage cancers is the real holy grail because surgery can cure up to 90 per cent of patients with early stage disease," he says.

"Cure rates decrease dramatically as the cancers become more advanced."

Lockett says it may not be a single chemical that the dogs are responding to, but a combination of chemicals present in specific proportions. He says the real test will be whether we can develop chemical detection systems sophisticated enough to detect the key volatile components.