Tuesday, November 20, 2012

Detecting Early Stage Lung Cancer May Become a Clinical Function of Sniffer Dogs

Lung cancer is one of the most deadly cancers, and one that all too often is not detected early enough for treatment to be effective. Although progress is being made, as discussed in the papers below, standard x-rays often fail to detect lung cancer early enough for any therapy to be successful. The fact that dogs are fairly good at detecting a significant proportion of lung cancers thus makes their use in a clinical setting a real possibility. As one of the studies discussed below concludes, canine cancer detection is “virtually on the verge of respectability.” Whether or when dogs will be used to screen us for lung cancer remains uncertain, but recent research indicates that the odds are going up in favor of this canine skill having practical application in the future.

I had speculated, as had Mary Elizabeth Thurston even earlier (1996), that remoteness might drive the use of dogs in cancer detection into clinical reality. The argument was made that dogs could become a tool of Doctors without Borders or doctors who fly to remote Arctic villages. Now it appears that the possibility of early detection by canines of cancers that are particularly difficult to find at asymptomatic stages may be the factor that brings dogs into actual diagnostic settings. This blog describes several articles, but the pictures were supplied by Dr. Tadeusz Jezierski of the Polish Academy of Sciences.

Dogs Distinguish Lung Cancer Patients from Healthy and COPD Patients

Breath Sample Tube
A team in Stuttgart, Germany (Ehmann et al., 2012), used four family dogs (two German shepherds, one Australian shepherd, and one Labrador retriever), two males and two females, all between 2.5 and 3 years old. All were trained to indicate to breath samples of patients with lung cancer by lying on the floor in front of the test tube and resting the muzzle against the tube.Training involved the dogs distinguishing breath samples of healthy volunteers from those of patients with lung cancer. No training was performed to distinguish COPD samples.

The researchers collected 220 breath samples from patients with COPD (50) or lung cancer (60), as well as from healthy individuals (110). Dogs were presented with five probes position in five separate retainers on the floor, rubber caps removed. The position of the probe with lung cancer was determined randomly and was blind to the participants except those who set up the probes.

The dogs did not perform identically, but each performed consistently. The accuracy of a dog’s indication did not favor advanced tumor stages. “The overall sensitivity was 71% and the specificity was 93%....” That is, the dogs identified 71% of the breath samples of those with cancer, and incorrectly found cancer in only 7% of the individuals who did not have cancer. The table, adapted from one included in the study, illustrates how specificity and sensitivity are calculated.

Breath sample without cancer
Breath sample with confirmed LC
Dogs indicating presence of LC
Dogs indicting absence of LC
372/400 = 93%


71/100 = 71%

The researchers concluded that there is “a stable marker (or scent pattern) that is strongly associated with LC [lung cancer] and independent from COPD, but can be reliably discriminated from tobacco smoke, food odors and (potential) drug metabolites.” They argue that sniffer dogs as cancer detectors are “virtually on the verge of respectability.”

What the dogs are identifying, according to the Stuttgart group, remains speculative. They note that 3,481 volatile organic compounds have been described in human breath, mostly in amounts of particles per trillion. Which ones increase because of lung cancer is only beginning to be described. Recent studies have succeeded in distinguishing healthy from cancerous breath by electronic nose technology. In these recent results, tumor stage did not influence the outcome in any of the studies, “implying that exhaled breath profiling has the potential to evolve as a screening test for LC—once specific markers have been identified.” They add that “it is currently difficult to predict when a clinically applicable diagnostic device for breath analysis will be available.”

As to specific chemicals the researchers noted that “Metropolol, Verapamil and Tiotropiumbromide were consistently distributed between LC and COPD patients, but not found in healthy volunteers. Marcumar, Clopidogrel and Ezetimib were present exclusively in COPD patients.”

As to COPD, the researchers note:

“COPD often precedes and accompanies LC in smoking patients…. COPD is characterized by typical lung function deterioration, chronic systemic and local airway inflammation and structural changes in lung parenchyma. It has been shown that the level of exhaled biomarkers is altered in patients with COPD compared to healthy control subjects…. Moreover, since the development of LC is much more frequent in COPD patients than in healthy controls, attention needs to be focused on the subtle differences in exhaled biomarker profiles between LC and COPD.”

Study Compares Dogs and Machines

As noted by Buszewski et al. (2012b), a sweetish, acetone-like breath odor indicates a person has diabetes, while the odor of rotten eggs, caused by organic sulfide and thiol compounds, suggests liver disease. Chemical analysis requires being able to deal with very low concentrations of chemicals exhaled so certain procedures must be used before analysis. The most common method of enriching volatile organic compounds involves solid-phase microextraction followed by analysis by gas chromatography (GC) or GC-mass spectrometry (GC-MS).

Taking Breath Sample
Exhaled air consists of alveolar air, which has been in contact with blood inside the alveoli, and ambient air, retained in the mouth, nose, pharynx, trachea, and bronchi. Alveolar air is strongest as the end of expiration of breath.

A chemical sensory approach, gas chromatography and mass spectrometry (GC-MS) for cancer screening was, in a second paper by the Polish team, Buszewski et al. (2012a), compared with using dogs to detect cancer. The GC-MS approach allows for specificity in the chemicals—volatile organic compounds, or VOCs—that are to be detected, whereas dogs are something of a “black box technology” with a yes/no response, where it is unknown what individual odor or combination of odors dogs are responding to. More specifically, the experiment used an Agilent 7890A gas chromatograph coupled with a Tru-TOF spectrometer. Male German shepherds, 20-22 months old, that had successfully completed a three-phase training in scent lineups were also used. Breath samples were collected from 44 healthy volunteers and 29 patients with lung cancer.

For the cancer scent lineups, one breath odor sample from a patient with lung cancer was placed in a line-up with four samples from healthy volunteers. Dogs had been taught to indicate the lung cancer sample by sitting down in front of it. Positions of odor samples in the line-up were randomly changed for every trial. Handlers accompanying dogs did not know the placement of the cancer sample in the line-up.

In the GC-MS testing, all compounds detect in breath samples were compared with ambient air samples, and only compounds with concentrations at least 10% higher than those in ambient air were reported. A number of compounds were higher, at a statistical level, in the breath of patients with cancer. These were butanal, 2-butanone, ethyl acetate, ethyl benzene, 2-pentanone, 1-propanol, and 2-propanol.

Breath Sample Prepared for Sniffing
As to the dogs, the researchers found:

“The dogs indicated correctly the pattern of breath samples from lung cancer patients with detection sensitivity and specificity of 82.2% and 82.4%, respectively. False positive indications toward healthy controls amounted to 17.8% of trials. The differences between dogs’ indications of cancer samples vs. controls were highly significant….” Thus, Buszewski et al. found lower specificity but higher sensitivity than the Stuttgart group described above.

Analysis of the data suggested that dogs may be particularly effective at detecting ethyl acetate and 2-pentanone. Chemical analysis of breath samples indicates that for ethyl acetate, breath exhaled by healthy persons has 1.12 to 8.22 parts per billion, while for cancer patients the range is 3.98 to 22.89 parts per billion. For 2-pentanone, the healthy range is 1.80 to 4.11 parts per billion, but 3.25 to 8.77 parts per billion for cancer patients. Nevertheless, that dogs are signaling to levels of these two compounds is not established. The researchers conclude that the odor signature that dogs use for discrimination “may be related to some specific qualitative or quantitative olfactory impressions produced by the mixture of VOCs.”

Where is This Going?

In an editorial that appeared in the same issue of the European Respiratory Journal that included the Stuttgart study, McCulloch et al. (2012) consider where such canine studies may be leading. They conclude that “the high accuracy of canine scent detection of lung cancer suggests dogs might, in the future, make some modest contribution to successes in lung cancer screening and detection.”

They note that lung cancer remains the leading cause of cancer death in the U.S., but that early detection remains a challenge. There are promising developments, including “the ongoing National Lung Screening Trail in the USA showing that lung cancer mortality can be reduced by up to 20% with low-dose spiral computed tomography (CT) screening compared to chest radiography…. At first diagnosis, over 75% of patients have advanced stage disease.”

Dr. Jezierski with Court, a Labrador Cancer Sniffer
McCulloch and his co-authors accept that “critics may turn up their nose at the mention of using sniffer dogs,” but they argue that high-quality papers have shown promising results. "The development of an ‘electronic nose’ for cancer detection has been underway for several decades; however, dogs still appear to be ahead in the race and seem to have sniffed their way to the front of the line.” The researchers invite us to imagine a future in “dogs could be used as a noninvasive preliminary diagnostic "screening tool or be used to help reduce false positives and false negatives of existing imaging technologies.”

Training Cancer Sniffers Will Change if Specific VOCs Are Identified

One could divide canine scent detection into two broad categories, those where dogs are trained to identify specific chemicals or groups of chemicals, and those where the dogs recognize and perhaps follow a scent which is sufficiently complicated that it is uncertain what chemicals or combination of chemicals are being recognized by the dogs. Thus, a dog trained to recognize accelerants—an arson dog—will be trained to identify certain combustible substances that may cause fires. Drug and explosive detection dogs are trained to recognize the odor of certain drugs or explosives, though these items may consist of groups of chemicals and it may sometimes be uncertain which one or which combination is of interest to the dogs. Then there are dogs, like cadaver dogs and human tracking dogs, that follow a trail or pursue a scent that may contain hundreds if not thousands of chemicals, and no pretense can be made at identifying exactly what chemicals, or ratio of separate chemicals, are being recognized by the dogs.

Cancer sniffers are, at the moment, in the second category, though the research by the Polish group may indicate that there will come a point where the volatile organic compounds that dogs recognize in the breath of cancer victims can be specified. This raises the possibility that cancer sniffing dogs may ultimately be trained on specific chemicals present in the breath of people with cancer and not present in those free of cancer, which may increase the reliability of the dogs in identifying cancer (and not indicating to the breath samples of people without cancer). Training procedures are simultaneously being refined, as described by Walczak et al. (2012).

The Black Box vs. the Smell-o-Matic

It is also possible that, even if dogs find a clinical function in cancer detection, the existence of this function may be transient since, once cancer VOCs are sufficiently identified, there will come a point when technology will provide accurate methods of measuring those chemicals. When that technology is available in the medical marketplace at a reasonable price, the dogs will no longer be necessary. If the portability of the technology remains a problem, then dogs might continue to be useful in remote areas, as Mary Elizabeth Thurston suggested almost two decades ago.

The black box effect of dogs is also part of why a technological solution may eventually be preferable for certain forensic functions that dogs perform. The presence of drugs inside of a house or a car, suggested by a dog’s indication to an odor it has been trained to detect, does not establish the amount of narcotics present, or even if they are present since the dogs may be detecting a residual odor. In oral argument before the Supreme Court in a case arising from use of a drug-sniffing dog in Florida, Florida v. Jardines, Justice Elena Kagan asked, if the police had a “smell-o-matic machine” that “alerted to the exact same things that a dog alerts to,” whether this could be brought to the front door of a suspected marijuana grow house the same way counsel was arguing could be done with a police dog. There is ongoing research on such technology, some of it overlapping the medical research discussed above, but there will likely be significant differences from a dog if the smell-o-matic is ever used in the field. First, it is likely to give a precise read on each chemical it is capable of detecting. It will not be a black box—an all or nothing indication—such as is given by a dog. Thresholds could be established based on detected levels that would more precisely reflect the probability of drugs being found within certain specified distances, humidity, wind level, air pressure, walls in between, etc., which would make the smell-o-matic more reliable than the dog.

The smell-o-matic might, for instance, be able to determine the amount of cocaine on a $20 bill, and whether its presence there is high enough on the surface to suggest recent contamination, and to distinguish such a bill from one that is innocently tainted from contact days or longer before. Although there is evidence that dogs do not alert unless the contamination is fairly recent, as discussed in a prior blog, a well-publicized study performed by the Miami Herald found that $20 bills supplied by Janet Reno, Jeb Bush and other prominent citizens had significant amounts of cocaine. As discussed in Police and Military Dogs, some courts remain reluctant to assign much significance to a drug dog’s alert in a currency forfeiture action.

The smell-o-matic would presumably be capable of detecting ambient levels of drugs in the atmosphere of an area, which if sufficiently concentrated might explain some residual odor indications by dogs. A recent paper determined that, in the air of Italian cities, cocaine and cannabinoids “are almost ubiquitous,” varying in concentration from a few pictograms to nanograms per cubic meter. The research found that the levels were greater in parts of Italy where drug consumption is thought by law enforcement to be higher than elsewhere. Thus, Cecinato et al. (2012) found that “cocaine ranged from 0.26 ng/m3 (Turin) and 0.21 ng/m3 (Naples) to 0.05 ng/m3 (Verona) and 0.02 ng/m3 (Palermo).” Curiously, part of the purpose of this research was to determine correlations between ambient cocaine levels and tumors, though the researchers state that much more testing is needed before they can reach conclusions in this area.

There is one other major difference between a dog and a smell-o-matic, though presumably this would seldom be a factor in the medical setting. That is, the handler of the dog in the medical setting operates without any expectation that the target odor smelled by the dog indicates cancer or not. Everything is double-blinded to the nth degree. Although this can be done in scent lineups conducted in forensic laboratories, in police field work, particularly at potential crime scenes, an officer uses his senses and experience to anticipate what criminal activity his investigation may uncover. Such expectations, when held by a canine handler, may allow for the possibility of intentionally making the dog alert (see the blog on The Good Wife and Breakfast in Collinsville) or unintentionally cueing the dog to alert. This problem could be eliminated with the smell-o-matic, which, once it is developed, may assure a measurably high reliability. The portability of the dog, as well as its psychological impact on criminals, may still argue for its use even if a small enough smell-o-matic is developed, however. In sum, the smell-o-matic may be less intrusive, because less likely to produce fruitless searches, than a dog. Admittedly, It will take some time for such a forensics tool to be developed and, given budgetary constraints, even more time to come into widespread use.

Gromit, Cancer Sniffer
Thanks to L.E. Papet for providing source materials. Thanks to Tadeusz Jezierski, a contributor to Police and Military Dogs, for sharing a slide presentation of recent research which includes the pictures used here. Also, thanks to the professor and his team for having the wisdom (or at least the sense of humor) to name one of the cancer sniffers Gromit, after Wallace's brilliant and long-suffering companion.

  1. Buszewski, B., Ligor, T., Jezierski, T., Wenda-Piesik, A., Walczak, M., and Rudnicka, J. (2012a). Identification of Volatile Lung Cancer Markers by Gas Chromatography-Mass Spectrometry: Comparison with Discrimination by Canines. Analytical and Bioanalytical Chemistry, 404(1), 141-6.
  2. Buszewski, B., Rudnicka, J., Ligor, T., Walczak, M., Jezierski, T., and Amann, A. (2012b). Analytical and Unconventional Methods of Cancer Detection Using Odor. Trends in Analytical Chemistry, 38, 1-12.
  3. Cecinato, A., Balducci, C., Romagnoli, P., and Perilli, M. (2012). Airborn Psychotropic Substances in Eight Italian Big Cities: Burdens and Behaviors. Environmental Pollution, 171, 140-147.
  4. Ehmann, R., Boedeker, E., Friedrich, U., Sagert, J., Dippon, J., Friedel, G., and Walles, T. (2012). Canine Scent Detection in the Diagnosis of Lung Cancer: Revisiting a Puzzling Phenomenon. European Respiratory Journal, 39, 669-76.
  5. Ensminger, J. (2010). The Cancer Sniffers. In Service and Therapy Dogs in American Society, Chapter 6. Charles C. Thomas, Springfield (summarizing pre-2010 research).
  6. Florida v. Jardines, Docket No. 11-564, U.S. Supreme Court, transcript of oral argument held October 31, 2012.
  7. McCulloch M., Jezierski T., Broffman M., Hubbard A., et al. (2006). Diagnostic Accuracy of Canine Scent Detection in Early- and Late-Stage Lung and Breast Cancers. Integrative Cancer Therapies 5(1), 1-10.
  8. McCulloch, M., Turner, K., and Broffman, M. (2012). Lung Cancer Detection by Canine Scent: Will There Be a Lab in the Lab? European Respiratory Journal, 39, 511-512.
  9. Thurston, M.E. (1996). Lost History of the Canine Race. Andrews and McMeell, Kansas City.
  10. Walczak, M., Jezierski, T., Gorecka-Bruzda, A., Sobczyniska, M., and Ensminger, J. (September 2012). Impact of Individual Training Parameters and Manner of Taking Breath Odor Samples on the Reliability of Canines as Cancer Screeners. Journal of Veterinary Behavior, 7, 283-294.

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