According to new research, they are able to sniff out lung cancer, a disease that estimates suggest will claim the lives of more than 150,000 people in the U.S. this year alone.
Researchers in Germany had a hunch that they could train dogs to pick up the scent of volatile organic compounds, or VOCs, which are linked to presence of lung cancer and released in the breath. So they collected breath samples from 220 volunteers, including people who were healthy, had lung cancer and had chronic obstructive pulmonary disease, and ran them through several tests with four dogs.
The canines -- two German Shepherds, an Australian Shepherd and a Lab -- were able to detect 71 out of 100 samples in which people did have lung cancer, and correctly identified 93 percent of the samples that were cancer-free.
"In the breath of patients with lung cancer, there are likely to be different chemicals to normal breath samples, and the dogs' keen sense of smell can detect this difference at an early stage of the disease," Dr. Thorsten Walles from Schillerhoehe Hospital and the author's lead study said in a statement.
This isn't the first time research has shown that dogs can sniff out cancer. Earlier this year, Japanese scientists reportedly trained a Black Lab to detect colorectal cancer with near perfect accuracy, and past studies have shown that dogs can smell skin, breast and ovarian cancer. A study from the journal PLoSOne found that dogs aren't the only super-sniffing animals either, suggesting that mice can also sniff out lung cancer, although they are more successful in the later stages. (Early detection is key in preventing lung cancer deaths.)
"Early on, I basically laughed the idea of cancer-sniffing dogs off," said Dr. Leonard Lichtenfeld, deputy chief medical officer for the American Cancer Society, who has blogged about the phenomenon for the organization.
"I am no longer a skeptic. It's an interesting idea that has some scientific rationale behind it, and it is worth pursuing," he added.
But both Lichtenfeld and the study's authors point out that there are difficulties in actually using dogs' superior sense of smell as a practical, widespread detection technique, because researchers still do not know exactly what compounds present in the breath of patients with lung cancer are a marker of the disease.
"If we target exactly what those volatile compounds are -- and there are lots of scientists working on that -- we may well turn this into a process or test that could show the presence of a cancer or recurrence of cancer." Lichtenfeld said. He was hesitant, however, to guess how far down the road that might be.
One additional roadblock could come in terms of training.
According to Dr. Bonnie Beaver, a past president of the American Veterinary Medical Association, it can be tough to train dogs in something like this, because humans can't smell what they're smelling. That makes it difficult to properly teach and reward them.
Another issue? The dogs have to want it.
"There has to be a drive to smell things, and that's not necessarily teachable through training," Beaver said, laughing that she could try training her own dog all she wanted, but it wouldn't work. "You can pick a breed that has a high likelihood of success, but it's individual, too. The dog has to be motivated."