Dogs sniffed out bowel cancer in more than nine out of 10 cases.
A Labrador retriever has sniffed out bowel cancer in breath and stool samples during a study in Japan.
The research, in the journal Gut, showed the dog was able to identify early stages of the disease.
It has already been suggested that dogs can use their noses to detect skin, bladder, lung, ovarian and breast cancers.
Cancer Research UK said it would be extremely difficult to use dogs for routine cancer testing.
The biology of a tumour is thought to include a distinct smell and a series of studies have used dogs to try to detect it.