Olfactory Detection of Human Cancer by Dogs. A Review of Research and Results

Olfactory Detection of
Human Cancer by Dogs:
A Review of Research Studies and
Results
Naomi O’Donoghue
BAAF2
Dundalk Institute of Technology

Contents
Introduction .................................................................................................................................1
Methodology................................................................................................................................ 2
The Results ..................................................................................................................................2
Untrained pets detectives .......................................................................................................2
Pickel et al. (2004) ................................................................................................................ 3
Willis et al. (2004)................................................................................................................. 3
McCulloch et al. ( 2006) ........................................................................................................4
Horvath et al. (2008).............................................................................................................. 5
Gordon et al. (2008) .............................................................................................................. 5
Horvath et al. (2010a)............................................................................................................ 5
Cornu et al. (2011) ................................................................................................................ 6
Sonoda et al. (2011)............................................................................................................... 6
Elliker et al. (2014)................................................................................................................ 7
Discussion and Recommendations .................................................................................................7
References ...................................................................................................................................9
Bibliography .............................................................................................................................. 10
Webography............................................................................................................................... 10
Appendix 1 ................................................................................................................................ 11
Table 1: Methods of Canine Training Compared.............................................................. 11
Appendix 2 ................................................................................................................................ 12
Table 2: Results of Studies Compared............................................................................. 12

1
Introduction
Every year, across the world, billions of dollars are invested into curing and preventing
cancer; the world’s leading cause of death. Advanced screening and detection methods are
developed and new drugs and technologies are trialled to help fight the many forms of this
disease. Yet still, the number of deaths caused by cancer continues to grow. Current figures
show that approximately 8 million people die from cancer each year and the World Health
Organisation predicts that this figure will increase 80% by 2030 (Centers for disease Contol
and Prevention, 2014).
Early detection may be man’s greatest from of defence. However, this is often difficult as
screening techniques can be expensive and in some cases are not without their own health
risks. In order to encourage people to seek regular care, less invasive, and simpler methods
would be advantageous, especially if they can prove to be more sensitive and accurate in
detecting early stages of cancer. This demand has led to many alternative methods and
technologies being explored.
The theory that dogs may be able to detect human cancer using their superior olfactory
system is one such alternative that has been widely researched in recent years. A dog’s sense
of smell is said to be anywhere from 1000 to 10,000 times more sensitive than humans.
Research has already shown that a dog can sense when an epileptic person is going to have a
seizure or when a diabetic’s blood glucose level drops. This is due to the dog’s ability to
smell pheromones or chemical changes taking place in the body (Spake, 2008).
Extensive training and tests have been carried out to discover if dogs can also be trained to
identify and detect human cancers. Findings from these studies have prompted scientists to
ask: what is it exactly that the dog can smell? Does cancer have a distinguishing odour
signature made up of Volatile Organic Compounds (VOCs) which are emitted into the air?
And if this chemical compound could be isolated and replicated then might it be possible to
develop an electronic nose which could potentially mimic the dog’s olfactory sense? It is
hoped to explore these ideas and attempt to answer the questions posed.

Naomi O’Donoghue Olfactory Detection of Human Cancer by Dogs BAAF2
2
Methodology
This review has been conducted to ascertain the validity of the hypothesis that dogs can smell
and be trained to smell cancer with a degree of accuracy great enough for diagnostic purposes
and worthy of an endeavour to replicate their skill electronically. Significant studies from the
past decade were explored. Efforts were made to include those studies which tested the
canine’s ability to identify a variety of cancers. Nine relevant studies were chosen under these
criteria. The contrasting training techniques, sample tissues used, and testing conditions were
examined and the results compared. The recorded accounts of untrained pet dogs who
“sniffed out” cancer in their owners have been included for comparison as they acted as the
catalyst for all future research into this topic.
The Results
Untrained pets detectives
Several cases tell the story of how pet dogs alerted their owners to the existence of cancer. It
began in 1989 with a letter to the British medical journal, the Lancet, which highlighted the
story of a woman who had been assured that a blemish on her upper leg was just a mole. Her
pet dog, showing an extraordinary interest in the mole, persisted in sniffing it for prolonged
periods and eventually tried to bite it off. This motivated the women to seek a dermatologist’s
opinion and a malignant melanoma was discovered. The authors were compelled to suggest
that the melanoma must have given off a scent that the dog could detect (Williams &
Pembroke, 1989).
Many years later, a man who had eczema on his leg for over 18 years had it re-examined after
his pet dog showed a bizarre interest in, and constantly sniffed at the lesion. Again it was
discovered to be cancer (Church & Williams, 2001). In yet another example, a pet dog poked
and nudged at its owners left breast until finally the women discovered a lump which a
biopsy later revealed as cancerous. In this case the dog’s interest never waned despite
mastectomy, chemotherapy and radiation, and the woman died a year later (Welsh, et al.,
2005).
What is important to note from these stories is that the dogs were not trained, there was no
reward for correct identification and the cancers were of different varieties. This possibly
suggests that the odour was so strong and at odds with what the dogs perceived as normal and
healthy that it provoked such a reaction. The intriguing potential of these claims led to the

3
numerous research studies to discover if dogs can definitely sniff out cancer and if the odour
emitted is from the cancer itself or manifested by the bodies attempt to fight against the
disease.
Pickel et al. (2004)
This study tested the ability of dogs to detect melanoma in real patients. Dogs were first
trained to recognise the scent of melanoma tissue cells and to associate this with praise from
the handler. The several stages of training showed promising results and so testing
commenced. (Please refer to Appendix 1 for a simple comparison of the training methods
used in all nine studies examined).
The final test stage involved seven real patients who were covered in a number of bandages,
one of which concealed the suspicious target area of skin. Dog A found the correct target on
six out of seven patients but failed to recognise any melanoma on the other. Dog B had a
success rate of three out of four and similarly did not identify any melanoma on the same
patient as Dog A. These results were deemed significant and the failure of both dogs on the
same patient showed consistency in their scent detection (Pickel, et al., 2004). The test
conditions displayed some flaws, however. It was not a double blind test and the patients or
the person who placed the bandages could have given the dog hints or cues. It can also be
argued that the numbers in the test group were too small. If healthy control patients had been
added and the dogs had correctly identified no target area it would have given more validity
to the results. One criticism is that the dogs’ response may not necessarily be to the actual
cancer, as one must examine a dog’s treatment of cuts or sores on their own skin and how
they often lick lesions on an owner. The changes in the skin itself may simply emit an odour
that the dog finds unusual (Horvath, et al., 2008).
Willis et al. (2004)
A “proof of principle study” was carried out to establish if dogs could successfully be trained
to locate bladder cancer with more accuracy than would be expected by “chance alone”
(Willis, et al., 2004). Urine samples were used in testing and controls were taken from both
healthy and diseased subjects. Efforts were made to attempt to match controls to cancer
samples as close as was possible by age and sex. They also included control samples from
patients who suffered with other urological disorders. This made for more accurate testing
conditions as any difference in scent that the dog picked up would be most likely due to the
cancer and not any other variable.

4
The dogs as a group had a success of 41% while mere chance was calculated at 14% (Willis,
et al., 2004). Their hypothesis was proven as the success rate was well over the probability of
it being just luck. (Please see Appendix 2 which compares the resulting data from all nine
studies in tabular form).
The study raises the issue of whether urine is the most appropriate sample to use in testing
and the training methods and selection of the dogs are open to criticism. Results, none the
less, showed positive findings that bladder cancer has an odour signature that dogs can
identify. Of particular note, and pointed out in the commentary of Cole, (2004), was that all
of the dogs indicated one control patient sample as positive for bladder cancer. This was of
such interest to the physician that tests were carried out on the subject and kidney cancer was
later discovered (Cole, 2004).
McCulloch et al. ( 2006)
This study proved that household dogs could be quickly trained to detect breast and lung
cancer using breath samples; that these dogs could discriminate cancerous samples over those
from control subjects; and that the dogs accuracy was unaffected by variables such as the
stage the cancer was at or whether the subject was a smoker (McCulloch, et al., 2006).
Sensitivity is the percentage of cancer targets that the dog correctly identifies, while
specificity is the percentage of control subjects that the dog correctly ignores. For the lung
cancer trials dogs scored 99% for both sensitivity and specificity. For breast cancer, results
were 88% and 98% respectively. This was the one of the first tests that showed such
successful and definitive results. One criticism was that the control samples used were all
from healthy individuals. Had controls been obtained from subjects with other non-cancerous
lung or breast conditions, sensitivity results may not have been so inflated (Moser &
McCulloch, 2010). Or perhaps, the dogs performance would have remained as high and more
credence could be attributed to their ability.
For experimental purposes, three patients who were in remission were used as control
samples. The dogs, however, indicated one of these controls as a cancerous target in 96% of
tests. A year and a half after the study the dogs’ diagnosis was confirmed, as breast cancer
was found to have recurred (McCulloch, et al., 2006).

5
Horvath et al. (2008)
Cancers such as ovarian carcinoma have unfavourable survival rates, which is why it is so
important to discover new techniques for early detection. Horvath et al. (2008) undertook
this study to examine the detection rate of ovarian cancer by trained sniffer dogs in a bid to
discover if the cancer has a specific signature. They argued that while results from previous
studies were encouraging, there was no definitive proof that the dogs were in fact receiving a
scent emitted directly from the cancer or if they were responding to other smells associated
with the body’s fight against it.
Moreover, they wanted to establish not only if the dogs could detect the cancer but if they
could then distinguish it from other gynaecological cancers. The dog’s sensitivity level was
an amazing 100%, detecting every target scent even when presented with other ovarian tissue
as controls. Their findings also indicate that ovarian carcinoma has a distinct and significant
odour which is different to other gynaecological cancers (Horvath, et al., 2008).
Gordon et al. (2008)
This study did not obtain the levels of success they had anticipated. Urine samples from
patients of breast and prostate cancer were used but the dogs in the tests did not show
significant detection rates. By their own admission, a more rigorous training discipline may
have produced better results. Each dog was trained at the trainers own home which allowed
for potential distractions and dogs were merely chosen on the basis of what breed the trainer
owned (Gordon, et al., 2008). Trainers did not work together and no regular or regimented
design was put in place which caused a lack of uniformity to occur. In a systematic review of
these 5 initial studies, Moser and McCulloch (2010) suggested that the discrepancies in the
training techniques adopted “may have made it nearly impossible for the dogs to perform
well” (Moser & McCulloch, 2010, p. 151).
Horvath et al. (2010a)
Building on their success and what was learned from the 2008 study; new tests were carried
out to include blood samples as well as tumour tissue samples. Again, they displayed an
efficient and apparently effective dog training technique. They proved that dogs can
differentiate between the blood from an ovarian cancer patient and the blood from a patient
suffering from other related cancers, “such as endometrial, cervical and vulvar carcinoma”
(Horvath, et al., 2010a). With these results the authors indicate that the distinguishing scent
discharged from the carcinoma is also detectable in the blood.

6
In another study by the author they successfully showcased the performance of an electronic
nose based on their 2008 findings that each cancer has a unique volatile organic compound.
The objective was for the device to detect, as the dog had, the ovarian carcinoma tissue
against healthy ovarian tissue based on the VOC that was being emitted. A sensitivity of
84.4% was achieved and a specificity of 86.8% (Horvath, et al., 2010b). Continuation studies
such as these, which build on the successes of previous work, contribute some of the most
significant data and results.
Cornu et al. (2011)
This study added to the now increasing list of cancers that dogs can be trained to detect.
Successful results were obtained for canine detection of prostate cancer, with both significant
sensitivity and specificity achieved (91% each). Theories established by previous studies that
perhaps urine was not an effective sample for use in testing could be dismissed with the
performance of the dog in this trial.
The training period and methods were thorough and a wide range of urine samples were used.
All 108 samples were given by men who has a biopsy of the prostate performed, the results
from which distinguished the cancer targets from controls. Of the 33 tests performed the dog
wrongly identified 3 control samples as targets. These were re-examined and 1 control
patient was found to have prostate cancer (Cornu, et al., 2011).
Sonoda et al. (2011)
While this study set out to train the dog to detect colorectal cancer, in the course of training
the dog learned to identify several cancer types. Initial training began with breath samples of
oesophageal cancer. The dog was allowed to smell the breath sample from the oesophageal
patient and then was instructed to find the cup which contained the same breath sample
amongst 4 control samples. This was repeated over the following days using lung cancer and
gastric cancer samples. In the next stage of training any 1 of those 3 cancer samples were
used at random. This then advanced to a stage where the dog was allowed to smell the sample
from 1 cancer and tasked to find another cancer type amongst the controls. Other cancer
types were introduced over time and by the end of training the dog could identify 12 different
forms of cancer (Sonoda, et al., 2011).
For both sample types a specificity of 99% was achieved and a sensitivity of 91% and 97%
respectively was achieved for breath and watery stool samples. Notably, results for colorectal

7
cancer in its early stage were also very precise. The excellent results and the advanced
training techniques suggest that much had been learned from previous studies.
Elliker et al. (2014)
In this most recent study, ten dogs were trained to identify prostate cancer. Several stages of
training took place followed by three test periods. While significant results were achieved in
training, levels of success in the actual tests were extremely poor. Only two dogs were
deemed good enough to progress to the test phase.
Sensitivity and specificity ratings achieved in the test period by the first dog were 13% and
71% respectively, and 25% and 75% for the second dog. The researchers believed that the
failure of the dogs to identify in tests what they could previously identify in training was
down to the fact that the dogs were not familiar with the new samples presented during the
test runs. 50 prostate cancer samples were used over the course of the training phase. They
suggest that the dogs may have “memorised the odour of each individual donor’s urine during
training” instead of learning the scent associated with the cancer in general (Elliker, et al.,
2014). The study by Cornu et al. (2011) discredits this theory that the dog memorised targets
samples, as 26 cancers were used during their training phase, and when the new, unfamiliar
samples were introduced in the testing phase, the dogs still achieved sensitivity of 91%.
In one stage of testing the dogs were rewarded whether they detected the target or not, as no
one in the room knew where the sample target lay. This was rectified in the next stage but
the author acknowledged that the dog’s decision making may have been confused by this
error which could have contributed to the poor success rates. The only other study examined
that displayed such poor results was Gordon et al. (2008) which similarly tested prostate
cancer using urine and also used 10 dogs in training. It is widely acknowledged that the poor
results were most probably due to the poor training structure, so this may also be the case in
this study. The failure of so many of the dogs to even make it past the training stage could
point to an ineffective training technique.
Discussion and Recommendations
Nine scientific studies and three anecdotal stories of dogs detecting human cancers have been
reviewed throughout this report. The primary objective was to discover if dogs could be
trained to detect human cancers and the overall combined findings reveal that they can.
Some studies displayed far superior training techniques and their results reflected this effort

8
with much greater success rates. Most studies used the reward-based clicker method to train
the dogs, which proved sufficient where it was adopted appropriately. The data does not
reveal any one breed, sex or age profile of dogs that showed the best results. Indeed, it is
difficult to compare the studies in this regard as successes or failures cannot solely be
attributed to the dog in isolation, but the many other variables such as design of training,
samples used and testing conditions must also be considered.
It was hoped to establish if each cancer contains volatile organic compounds and a unique
chemical signature. Several of the studies claimed evidence of this to be true. However,
while we now know of their existence, research has still not been able to decipher what
exactly this chemical make-up is. The establishment of a more concrete breakdown of
chemical configurations and biomarkers was expected by this author due to the profound
leaps forward in science and technology over the last twenty years. However, data found in
this area was somewhat disappointing. Still, advances are being made which will undoubtedly
lead to a break-through in the future.
With regard to the sample types used, the exhaled breath and tumour tissue appears to give
the highest success rates. This author would suggest that breath samples may be the most
advantageous, non-invasive and cost effective means of cancer testing if the work that is
being carried out on electronic noses continues to a prototype stage. Results from the Horvath
et al. (2010b) study incite confidence that the dogs’ sense of smell will one day be fully
replicated with substantial sensitivity. Perhaps in the future, blowing into a cancer
breathalyser will be a routine procedure carried out at every G.P. visit and cancers will be
caught at their early stages.
These studies all stemmed from one occurrence where a dog potentially saved its owners life
by sniffing out a skin cancer (Williams & Pembroke, 1989). A significant number of cases
were found where volunteers who had simply given samples to be used as controls were
discovered to have cancer. These people may be alive today due to the fact that this research
is being carried out. So, while cancer sniffing dogs may not yet have advanced to the stages
where they are being used in practical work conditions like other explosive and narcotic
sniffer dogs, they have, none-the-less, already started their life saving work. One is left in no
doubt that dogs really are man’s best friend!

9
References
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Available at:http://www.cdc.gov/cancer/dcpc/resources/features/worldcancerday/
[Accessed02 April 2014].
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Cole,T.,2004. Commentary:Teachingdogsnew tricks. BJM, Volume329, p.718.
Cornu,J. etal.,2011. OlfactoryDetectionof Prostate CancerbyDogs SniffingUrine:A StepForward
inEarly Diagnosis. European Association of Urology, 59(2),pp.197-201.
Elliker,K.etal.,2014. Keyconsidertionsforthe experimentaltrainingandevaluationof cancer
odourdetectiondogs:lessonslearntfromadouble-blind,controlledtrial of prostate cancer
detection. BMCUrology, Volume14,p. 22.
Gordon,R. et al.,2008. The Use of Caninesinthe Detectionof HumanCancers. The Journalof
Alternativeand Complementary Medicine, 14(1),pp.61-67.
Horvath,G., Andersson,H.& Paulsson,G.,2010a. Characteristicodourinthe bloodrevealsovarian
carcinoma. BMC Cancer, Issue 10, p. 643.
Horvath,G., Chilo,J.& Lindblad,T.,2010b. Differentvolatilesignalsemittedbyhumanovarian
carcinomaand healthytissues. FutureOncology, 6(6),pp.1043-1049.
Horvath,G., Jarverud,G.,Jarverud,S.& Horváth,I.,2008. Human OvarianCarcimonaDetectedby
SpecificOdor. IntegrativeCancerTherapies, Issue 7,pp.76-80.
McCulloch,M. et al.,2006. DiagnositcAccuracyof Canine ScentDetectioninEarly- andLate-Stage
Lung and BreastCancers. IntegrativeCancerTherapies, 5(1),pp. 30-39.
Moser,E. & McCulloch,M., 2010. Canine scentdetectionof human cancers:A review of methods
and accuracy. Journalof Veterinary Behavior, Issue 5,pp.145-152.
Pickel,D.etal.,2004. Evidence forcanine olfactorydetectionof melanoma. Applied Animal
BehaviourScience, Volume 89,pp. 107-116.
Sonoda,H. etal.,2011. Colorectal cancerscreeningwithodourmaterial bycanine scentdetection.
Gut, 60(6), pp.814-819.
Spake,A.,2008. Could a Dog SaveYourLife?. [Online]
Available at:http://www.diabetesforecast.org/2008/mar/could-a-dog-save-your-life.html
[Accessed 06 April 2014].
Welsh,J.,Barton,D. & Ahuja,H., 2005. A case of breastcancer detectedbya petdog. Community
Oncology, Issue 2,pp.324-326.
Williams,H.&Pembroke,A.,1989. Snifferdogsinthe melanomaclinic?. Lancet, Volume 1,p.734.

10
Willis,C. etal.,2004. Olfactorydetectionof humanbladdercancerbydogs:proof of principle study.
BMJ, Volume 329, pp.712-718.
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histocompatibilitycomplex-dependentodourcomponents? –A possible cure anda precocious
diagnosisof cancer. Medical Hypotheses, 66,pp.270-272.
King,C.R.2006. Dogs May Be Able toDetectCancer. Oncology Nursing Forum, 33(1),pp.21-22.
Lippi,G. 2011. Letterto the Editor. European Association of Urology, 60(4),p.29
Roine,A.etal.,2012. Detectionof smell printdifferencesbetweennonmalignant andmalignant
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[Accessed7April 2014].
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11
Appendix 1
Table 1: Methods of Canine Training Compared
Breed of Dog(s)
Age and Sex of
dog
Number of Dogs
trained and used
in testing
Dog’s previous
training history
Method of dog
training
Length of training
Picket et al.
(2004)
Standard Schnauzer
Retriever Bitch
4 year old male
6 year old bitch
2
Certified bomb
detection dog and
Master Hunter
Not indicated
Several weeks and
Less than several
weeks
Willis et al.
(2004)
Variety of breeds Not indicated 6
No previous search or
scent training
Clicker training 7 months
McCulloch et al.
(2006)
3 Labrador
retrievers
2 Portuguese water
dogs
7-18 months
3 dogs, 2 bitches
5 No previous training
Food reward-based
clicker training
2-3 weeks
Horvath et al.
(2008)
Riesenschnauzer 4 years old 1 Not indicated
Resembled sniffer
dog training
12 months – twice
per week
Gordon et al
(2008)
Various Breeds 2-8 years old 10
Most had previous
training
Clicker training with
food reward
12-14 months
2-7 times per week
Horvath et. al.
(2010)
Black Giant
Schnauzer
7 year old bitch
3 year old bitch
2
Previously trained to
detect ovarian
carcinoma
No previous training
Resembled sniffer
dog training
9 months
Cornu et. al.
(2011)
Belgian Malinois
Shepherd
Young Dog 1 No previous training
Clicker Training
with ball reward
24 months – 5 days
per week
Sonoda et. al.
(2011)
Labrador retriever 8 year old bitch 1
Trained in water
rescue and then as a
cancer detection dog
Play reward-based
approach
Not indicated
Elliker et. al
(2014)
7 different breeds
1-11 years old
4 bitches and 6 dogs
10 and 2
No previous odour
detection training
Food reward-based
clicker training
5-13 months

12
Appendix 2
Table 2: Results of Studies Compared
Cancer tested Sample type Structure of test
Sensitivity /
Specificity
or Success rate
Cancer : Control
Picket et. al.
(2004)
Melanoma Melanoma tissue cells Single Blind 75-85.7% success 1:7-29
Willis et. al.
(2004)
Bladder Urine and dried urine Single Blind 41% success 1:6
McCulloch et. al.
(2006)
Lung and Breast Exhaled breath Double Blind 99/99% and 88/98% 1:4
Horvath et. al.
(2008)
Ovarian Tumour tissue Double Blind 100/97.5% 2:8
Gordon et. al
(2008)
Breast and Prostate Urine Blinded but unspecified
22/18% Sensitivity and
17% success
1:6
Horvath et. al.
(2010)
Ovarian Blood and tumour tissue Double Blind 100/98% and 100/95% 1:5
Cornu et. al.
(2011)
Prostate Urine Double Blind 91/91% 1:5
Sonoda et. al.
(2011)
Colorectal
Exhaled breath and
watery stool samples
Double Blind 91/99% and 97/99% 1:4
Elliker et. al
(2014)
Prostate Urine Double Blind 13/1% and 25/75% 1:3

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