Scientists’ interest in dogs as cancer detectors began a dozen years ago with a case report that a household pet appeared to sniff out its owners’ melanoma. Another woman claims her dog became obsessed with her right breast, leading to the discovery of a cancerous lump. The evidence just keeps mounting that ordinary household dogs can be trained to use their noses to detect various kinds of cancer with near- perfect accuracy.
Researchers at Schillerhoehe Hospital in Germany trained four dogs – two German shepherds, an Australian shepherd and a Labrador – to detect lung cancer. Three groups of patients were tested: 110 healthy people, 60 with lung cancer and 50 with chronic obstructive pulmonary disease (COPD), a narrowing of the airways of the lungs. They all breathed into a fleece filled tube, which absorbed any smells. The dogs sniffed the tubes and sat down in front of those in which they detected lung cancer smells.
The dogs correctly identified 71 positive lung cancer samples out of a possible 100, the researchers write in the European Respiratory Journal. They also correctly identified 372 non-cancerous samples out of a possible 400.
It is unclear what exactly makes dogs such good smellers, though much more of the dog brain is devoted to smell than it is in humans. Canines also have a greater convergence of neurons from the nose to the brain than humans do. They have 220 million olfactory (smell) receptors, compared to our meager 5 million, so they can sniff out mere molecules of certain substances.
It is thought that tumors produce “volatile chemicals” which a dog can detect. What’s interesting about this is that the dogs were able to detect cancer even in the presence of other factors, like tobacco smoke and COPD. Current lab tests for lung cancer can’t do this. This suggests that there is indeed a VOC (volatile organic compounds) associated directly with lung cancer, which can be detected — at least by a dog — even in the presence of other compounds. VOCs are emitted from the surface of cells as they undergo tumor-induced gene and protein changes. Identifying the VOCs that certain cells make can go a long way toward early diagnosis, when a scan might not be able to detect anything.
In the latest study, published in the peer-reviewed journal Gut, Japanese researchers report that an eight-year-old black Labrador was 97% accurate in detecting colon cancer, nearly as accurately as a colonoscopy. The dog was given breath and stool samples of 306 patients, collected right before they received colonoscopies; 48 patients had recently been diagnosed with bowel cancer, and the other 258 were either suffering from another colorectal ailment or had survived cancer, or were healthy.
The dog was almost as good at spotting cancer in breath samples. When smelling breath samples, the dog was at least 95% as accurate at identifying cancer as colonoscopy, and 98% correct when sniffing stool samples, the researchers found. Most impressively, the dog was especially good at spotting early stage cancer, and could discern polyps from malignancies, which colonoscopies can’t do.
“Most striking is the ability of the dogs to detect bowel cancer at its earliest stages,” Trevor Lockett, a bowel cancer researcher with the Commonwealth Scientific and Industrial Research Organisation in Australia, said in an e-mail. Most current non-invasive tests for bowel cancer identify later-stage disease far more efficiently than early-stage, Lockett said. “Detection of early-stage cancers is the real holy grail in bowel cancer diagnosis because surgery can cure up to 90 percent of patients who present with early-stage disease,” he said.
You may not be greeted by a dog when you go in for cancer screening any time soon. But researchers hope that these findings will be able to help them design new ways to detect cancer by incorporating some kind of smell-detecting method.