Dogs Can Smell Lung Cancer in Humans
In its early stages, lung cancer has few symptoms, making it difficult for doctors to catch it early when it’s still treatable. “This is the holy grail,” says Suresh S. Ramalingam, associate professor and director of the lung program at Emory University’s Winship Cancer Institute in Atlanta.
“The whole field is focused on using something that’s readily available that does not involve an expensive surgery or scan that would allow us to find early cancers,” says Ramalingam, who is developing technology that aims to replicate the ability of dogs to smell trace amount of chemicals produced by cancerous tumors. He was not involved in the research.
Recently a large, government-funded study found that longtime smokers at high risk for lung cancer who received annual rapid computed tomography (CT) scans of their lungs cut their risk of dying of the disease by 20%. But that test has caused controversy because it falsely detects cancer in about one out of four people, leading to further invasive procedures.
Checking for Lung Cancer
A study published in the European Respiratory Journal found that four trained dogs — two German shepherds, an Australian shepherd, and a Labrador retriever — correctly identified cancer in 71 of 100 samples from lung cancer patients.
They also ruled out cancer in 372 out of 400 samples that were known not to have cancer, giving them a very low rate of false positives, about 7%. “The surprising result of our study is the very high specificity of our dogs to identify lung cancer,” says study researcher Thorsten Walles, MD, a lung surgeon at Schillerhoehe Hospital in Gerlingen, Germany.
“It even surpasses the combination of chest computed tomography (CT) scan and bronchoscopy, which is an invasive procedure that needs some form of anesthesia,” Walles tells WebMD in an email.
Doctors have previously reported cases in which dogs have alerted their owners to undiagnosed skin, breast, and lung cancers by repeatedly pawing or nosing an affected body part. Some dogs have even been trained to smell low blood sugar levels in people who have diabetes.
But dogs have had more mixed success in carefully controlled studies, where samples from healthy people and sick people have been mixed. A study published in BMJ in 2004 found that dogs correctly identified bladder cancer an average of about 40% of the time, a rate that was better than the 14% accuracy that could be expected by chance but was lower than available tests.
But in June, researchers in Japan reported that dogs could detect the presence of colon cancer in human breath and stool samples with nearly 90% accuracy, a success rate only slightly lower than colonoscopy.
How Dogs Detect Cancer
Researchers think dogs and other animals are able to smell disease by picking up on minute changes in compounds called volatile organic compounds (VOCs) that comprise chemical signatures in the body.
As many as 4,000 different VOCs, for example, have been identified in human breath.
A dog’s sense of smell has been estimated to be 100 to 1,000 times more powerful than a human’s, says Gary K. Beauchamp, Ph.D., director of the Monell Chemical Senses Center in Philadelphia.
“It’s not just how sensitive their nose is. It’s how they process this into a recognition pattern,” Beauchamp says. “The reason dogs can do this is that they’re recognizing a complex picture, and that’s the big trick, to find out how to mimic that in some sort of device that could be useful for diagnostic purposes in human disease.”
Ramalingam says because success rates vary between dogs and between samples, the real value of knowing dogs can detect cancer will likely be in building technology that can reliably repeat what they can do.
“The dogs show that it can be done. We need to find out what the dogs are sniffing so we can do it in a more scientific manner.”