Dogs can sniff out bowel cancer in breath and stool samples, with a very high degree of accuracy - even in the early stages of the disease - reveals research published online in the journal Gut.
The findings prompt the authors to suggest that chemical compounds for specific cancers circulate throughout the body, which opens up the prospect of developing tests to pick up the disease before it has had the chance to spread elsewhere.
A specially trained Labrador retriever completed 74 sniff tests, each comprising five breath (100 to 200 ml) or stool samples (50 ml) at a time, only one of which was cancerous, over a period of several months.
The samples came from 48 people with confirmed bowel cancer and 258 volunteers with no bowel cancer or who had had cancer in the past.
Around half of the volunteer samples came from people with bowel polyps, which although benign, are considered to be a precursor of bowel cancer. And 6% of the breath samples and one in 10 of the stool samples from this group came from those with other gut problems, such as inflammatory bowel disease, ulcers, diverticulitis, and appendicitis.
The bowel cancer samples came from patients with varying stages of disease, including early stage.
The dog successfully identified which samples were cancerous, and which were not, in 33 out of 36 breath tests and in 37 out of 38 stool tests, with the highest detection rates among those samples taken from people with early stage disease.
This equates to 95% accuracy, overall, for the breath test and 98% accuracy for the stool test, compared with conventional colonoscopy - a procedure involving a tube with a camera on the end inserted through the back passage.
Samples from smokers or from those with other types of gut problems, which might be expected to mask or interfere with other smells, did not pose a problem for the dog.
This indicates that there are specific discernible odours given off by cancer cells which circulate around the body, say the authors. And it is backed up by other research and anecdotal evidence indicating that dogs can sniff out bladder, skin, lung, breast and ovarian cancers, they add.
The authors concede that using dogs to screen for cancers is likely to be impractical and expensive, but a sensor could be developed to detect the specific compounds.
The faecal occult blood test, which picks up hidden blood in a stool sample is an effective and non-invasive method of screening for bowel cancer, say the authors, but it is only able to pick up early stage disease in one in 10 cases.
"Early detection and early treatment are critical for the successful treatment of cancer and are excellent means for reducing both the economic burden and mortality [of bowel cancer]," comment the authors.