Dogs can detect bowel cancer even in the early stages just by smelling the breath or stool of a patient, according to a new study.
While dog-based cancer detection is too expensive and unwieldy to work on a large scale, the findings could help researchers identify the chemical compounds that dogs detect. Tests for those compounds may be more effective than current diagnostic methods, Japanese researchers reported online Jan. 31 in the journal Gut.
"In the future, studies designed to identify cancer-specific volatile organic compounds will be important for the development of new methods for the early detection of CRC [colorectal cancer]," the researchers wrote.
Colorectal cancer refers to cancer of the large intestine (colon) and rectal cancer, or cancer of the lower region of the colon. In the United States, it is the fourth most common cancer in men and women, according to the National Cancer Institute.
The nose knows
Dogs are known for their amazing noses, which enable them to sniff out a variety of cancers. Pooches of several breeds have been taught to identify prostate cancer, as well as cancers of the skin, lungs, breasts, ovaries and bladder. Usually, dogs require just a whiff of a person's breath (or in the case of bladder cancer, urine) to identify disease. After training, many dogs can accurately catch even early-stage cancers.
In the latest study, researchers collected breath and stool samples from 48 patients with colorectal cancer, 203 people without the disease, and 55 people with a previous history of cancer, but who didn't have any active cancers at the time. Stool samples were collected during colonoscopies, and patients breathed into specially designed bags to capture a sample of their breath.
Next, a trained 8-year-old Labrador retriever sniffed the samples. When she detected cancer, the dog was trained to sit in front of the sample. Her reward for a right answer: a game of fetch with a tennis ball.
The researchers measured both the dog's ability to correctly identify cancerous samples and her ability to ignore cancer-free samples. In both cases, she was very accurate, correctly identifying 91 percent of cancerous breath samples and 97 percent of cancerous stool samples. The dog ignored 99 percent of both cancer-free breath samples and cancer-free stool samples.
The dog's accuracy held even in cases where the patient was a smoker or had other potentially aromatic bowel diseases.
What's that smell?
Still, it takes years and lots of cash to train a cancer-sniffing dog, so don't expect Dr. Rover at your bedside anytime soon. The promise of the research, the authors wrote, is to identify volatile (able to easily vaporize) compounds given off by cancer.
In this case, the researchers ruled out the possibility that dogs were cuing into changes in certain blood proteins. Previous research has indicated a few compounds of interest, the researchers wrote.
The next step is to test those compounds both with chemical analysis and with cancer-sniffing canines.
You can follow LiveScience Senior Writer Stephanie Pappas on Twitter @sipappas.