Dogs can be trained to accurately sniff out lung cancer, a German study suggests.
Lung cancer is a common cause of death worldwide. In Canada, more than a quarter of all cancer deaths are attributed to lung cancer, and it remains the second most common cancer in both men and women, according to the Canadian Cancer Society.
Early detection of lung cancer is often just by chance, in part because the disease has few symptoms, but prognosis depends on early diagnosis. Scientists are working on trying to detect it using exhaled breath samples, but results have been elusive.
Now researchers writing in the European Respiratory Journal say they were able to train four household dogs to distinguish between breath samples from lung cancer patients and those of healthy people, based on scent alone.
Thorsten Walles from Schillerhoehe Hospital in Gerlingen, Germany, and his co-authors say the two German shepherds, one Australian shepherd dog and one Labrador retriever were able to distinguish between breath samples from people with lung cancer and from those with chronic obstructive pulmonary disease, or COPD.
"This meticulous characterization of 125 breath samples tested by four sniffer dogs confirms the existence of a stable marker (or scent pattern) that is strongly associated with lung cancer and independent from COPD, but can be reliably discriminated from tobacco smoke, food odours and (potential) drug metabolites," the study's authors concluded.
In the study, the dogs successfully identified 71 samples with lung cancer out of a possible 100. They also correctly detected 372 samples that did not have lung cancer out of a possible 400.
Passing the sniff test
The dogs' keen sense of smell seemed to detect different chemicals in the breath of patients with early stage lung cancer, Walles said.
Compared with humans, dogs have an extraordinary sense of smell. A bloodhound can detect a scent four days old with a nose said to be a million times more sensitive than a human's.
To screen for lung cancer non-invasively, researchers would need to precisely identify the compounds in the exhaled breath of lung cancer patients.
"Our results confirm the presence of a stable marker for lung cancer. This is a big step forward in the diagnosis of lung cancer, but we still need to precisely identify the compounds observed in the exhaled breath of patients. It is unfortunate that dogs cannot communicate the biochemistry of the scent of cancer," Walles said in a release.
The researchers suggested that integrating sniffer dogs into lung cancer screening research might help.
"What is probably going on here is that the cancer is producing something we call volatile compounds," said Dr. Len Lichtenfeld, deputy chief medical officer with the American Cancer Society in Atlanta.
"That is sort of like a gaseous compound that's in the blood, comes up into the lung, gets exhaled into the breath and the dogs are able to detect it. The question I think for the future will be if we can develop this sniffing test, so to speak. Will it be better or more accurate or at least as accurate as we can achieve with a CT scan? And we just don't know that at this point in time."
The study's authors said it would not have been possible "without the docility and excitement of 'Kessie,' 'Benny,' 'Hector' and 'Bonnie.'"
During the experiment, two observers who did not know which samples were cancerous recorded the dogs' indications. To identify a cancerous sample in a test tube, a dog had to lie in front of it without hestitation.
In 2006, researchers in California also reported that sniffer dogs could accurately diagnose lung cancer from patients' breath samples. But that study might have been biased by odours related to other diseases, therapies and smoking, Walles and his co-authors said.
In the latest study, sniffer dogs were able to identify lung cancer with an overall sensitivity of 71 per cent, which reflects how well a test correctly identifying people who have a health problem and how many cases are missed.
The dogs also showed a specificity of 93 per cent, which reflects how good a test is at correctly identifying people who are well.
Three of the study's authors funded the research themselves.
About 24,200 new cases of lung cancer and 20,600 deaths were estimated for 2010 by the Canadian Cancer Society.