A dog trained to sniff out colorectal cancer was almost as accurate as a colonoscopy in a study that suggests less invasive tests for the disease may be developed.

The Labrador retriever was at least 95 percent as accurate as colonoscopy when smelling breath samples and 98 percent correct with stool samples, according to the study, published today in the medical journal Gut. The dog’s sense of smell was especially effective in early-stage cancer, and could discern polyps from malignancies, which colonoscopy can’t.

The results point to the existence of volatile organic compounds that might be the basis for non-invasive, early colorectal cancer diagnostics, wrote the researchers led by Hideto Sonoda of Kyushu University in Japan. Colonoscopies involve inserting a tube with a camera through the rectum, and less-invasive fecal blood tests only detect early-stage disease in one out of 10 cases, they wrote.

“Most striking is the ability of the dogs to detect bowel cancer at its earliest stages,” said Trevor Lockett, a bowel cancer researcher with the Commonwealth Scientific and Industrial Research Organisation.

Most current non-invasive tests for bowel cancer identify later-stage disease far more efficiently than early-stage, Lockett said.

Labrador retrievers, originally used in Canada to catch fish and pull in nets, now work as guide dogs for the blind, search-and-rescue animals and narcotics detectors.