Nose for Bad News Scientists Sense Strong Potential in Cancer-sniffing Canines

The concept of using dogs to sniff out cancer has been anecdotally popular for years, but new studies are putting solid science behind the success stories.

For instance, sniffer dogs could be used for the early detection of lung cancer, according to new research published in the European Respiratory Journal.

The study, carried out by researchers from Schillerhoehe Hospital in Germany, is the first to find that sniffer dogs can reliably detect lung cancer — the most common cause of death from cancer worldwide.

“This is the holy grail,” Dr. Suresh S. Ramalingam, associate professor and director of the lung program at Emory University’s Winship Cancer Institute in Atlanta, told WebMD recently.

“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,” added 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.

The disease is not strongly associated with early symptoms, and early detection often occurs by chance, the German report notes. Current methods of detection are unreliable, and scientists have been working on using exhaled breath specimens from patients for future screening tests.

This method relies on identifying volatile organic compounds (VOCs) that are linked to the presence of cancer. Tumors produce specific VOCs, which pass into the bloodstream. The lungs create a bridge between the bloodstream and airways, so the breath exhaled by a patient will carry the VOC signatures of a tumor if one is present.

Although many different technological applications have been developed, this method is still difficult to apply in a clinical setting as patients aren’t allowed to smoke or eat before the test, sample analysis can take a long time, and there is also a high risk of interference. Because of these reasons, no lung cancer-specific VOCs have yet been identified.

The study attempted to assess whether sniffer dogs could be used to identify a VOC in the breath of patients. The researchers worked with 220 volunteers, including lung-cancer patients, chronic obstructive pulmonary disease (COPD) patients, and healthy volunteers. They used dogs that had been specifically trained.

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. Importantly, they were able to detect lung cancer independently from COPD and tobacco smoke.

“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, said the study’s author, Dr. Thorsten Walles from Schillerhoehe Hospital. “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,” he quipped, “that dogs cannot communicate the biochemistry of the scent of cancer.”

Sniffing for Answers

The European study is far from the only such research being conducted.

Last year, Japanese scientists reported training a Labrador retriever named Marine to sniff out colorectal cancer with up to 98{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} accuracy, according to ABC News. Those results are far more accurate than some tests currently used to diagnose the cancer, such as the fecal occult blood test, which accurately predicts the condition around 10{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} of the time.

To develop their study, these researchers considered previous research showing that dogs have the ability to sniff out cancer in patients’ breath, according to National Geographic. Using this idea, the Lab was trained to sit in front of samples that contained signs of cancer.

ABC noted that a dog’s sense of smell is up to 1 million times better than a human being’s, but not all dogs have the same abilities. “You don’t see bomb-sniffing pugs,” Dr. Marty Becker, a veterinarian at the North Idaho Animal Hospital, told the network. “You’ve got to have pretty robust olfactory capabilities.”

Although the suggestion of cancer-sniffing canines first appeared in a medical journal in 1989, few follow-up studies were undertaken over the next decade-plus. But around 2004, such initiatives became more common.

The question that inevitably follows, of course, is how dogs fit into cancer prevention and treatment. Some researchers have suggested that they may be integrated directly into patient care, similar to their use in detecting bombs, drugs, and missing people.

Others say dogs specially trained to sniff out cancer may be better-used in labs, where gas chromatographs could be used to isolate which specific compounds the dogs identify.

“The problem with cancer-detecting dogs is that, well, they’re dogs,” writes Ashlee Vance for Bloomberg News. “Hospitals haven’t embraced the idea of a diagnostic tool that poops, barks, and requires feeding.”

But technology startups, she said, have been scrambing to build digital devices that can mimic the dogs’ olfactory sense and reduce the need for biopsies and CT scans.

Metabolomx, based in California, is one company on track to bring a cancer-sniffing device to market. The firm’s device looks like a computer with a hose attached. When a patient breathes into it for a few minutes, the machine analyzes the breath and its VOCs.

“It may seem surprising, but it’s actually very straightforward,” Paul Rhodes, the co-founder and CEO at Metabolomx, told Bloomberg.

Dr. Peter Mazzone, a lung-cancer expert at the Cleveland Clinic, recently published results from a trial he ran with an early version of the Metabolomx machine. He studied 229 people and found that the machine could detect lung cancer more than 80{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} of the time.

The machine also outdid canine studies by distinguishing between different forms of lung cancer with about 85{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} accuracy. The goal, he said, is to use a more-sensitive, updated version of the machine in new trials and see if it can reach 93{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} accuracy — a figure doctors say would make the device viable for widespread use.

Making Scents of It All

Michael McCullough welcomes such efforts. A researcher at the Pine Street Foundation in California, he was part of a study that trained five different dogs to smell breast and lung cancer on a patient’s breath. The dogs’ diagnoses were 88{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} to 99{06cf2b9696b159f874511d23dbc893eb1ac83014175ed30550cfff22781411e5} accurate, even when olfactory factors like smoking were taken into account.

Figuring out how they do it, he told Science Update, could pave the way for new technologies that could screen for cancer with a simple breath test.

“The fact that it was dogs is almost beside the point,” he said. “Although I should add that the dogs performed so well that now technology really has to rise to the challenge that they laid down.”