This news story is racing around the world this week: A specially trained dog in Japan correctly detected more than 95 percent of people who had colorectal cancer—even early cancers—just by sniffing breath or stool samples.
Not surprising that the media have jumped on it: It’s a cute story and hopeful. But many reports are missing the real point: Rather than replacing colonoscopies with dog-staffed screening clinics, the real goal is to find lab tests that could detect cancer much earlier.
The Japanese study, published in the peer-reviewed journal Gut, in which a dog detected colorectal cancer in breath as well as stools indicates that cancer chemicals might circulate throughout the body. This nudges basic science another step toward identifying one or more organic chemicals present in cancer that might be detectable by simple lab tests.
The dogs are way ahead of humans: They have 220 million olfactory (smell) receptors, compared to our measly 5 million, so they can sniff out mere molecules of certain substances.
Trained for three years in a special Japanese school, the Labrador retriever could already detect 12 types of cancer in breath and tissue samples before she joined the colorectal cancer study in 2008. Medical researchers created a careful, double-blind trial using breath and stool samples (taken during colonoscopy) from 320 healthy people and 40 patients with CRC. After letting the dog sniff breath samples from a colorectal patient, they then gave her five different samples at a time. When she correctly “sat” in front of a positive sample, she was rewarded by a tossed tennis ball to fetch. She correctly identified 33 of the 36 breath samples from cancer patients; and 37 of the 38 stool samples. She correctly ignored 99 percent of the healthy samples.
Comparing the results to colonoscopies and FOBT samples for blood in stools showed that the dog wasn’t confused by the presence or absence of blood, benign polyps, or inflammatory bowel disease.
However, the dog could not detect precancerous polyps found by colonoscopy.
Other small trials have shown dogs capable of detecting certain cancers. What this and other small trials showing similar results with other dogs point to—is that cancer, or at least classes of cancer, appear to have VOC, or volatile organic compounds, that can be detected. (Volatile means the molecules can become airborne—thus smell-able.)
The Japanese researchers did point out that this is not a step toward mass dog-screening, because dogs’ abilities vary, from each other and even day by day. But the dogs may help find testable organic compounds, further explaining the basic biology of cancer.
- Like most scientific news, this is just one step forward on a promising path of research.
- Man has a lot to learn from other animal species (and plants and even single-celled organisms). In tight economic times, it might be easy to cut funding for odd-sounding basic research…but it seems that Man’s Best Friend might have something to teach us.
SOURCE: Gut published online January 31, 2011, doi: 10.1126/gut.2010.218305.
Read the full study at (http://gut.bmj.com/content/early/2011/01/17/gut.2010.218305.full.pdf).