Monday April 13 2015
Could your dog sniff out a disease?
"Dogs trained to detect prostate cancer with more than 90% accuracy," The Guardian reports. Two trained bomb-sniffing dogs also proved remarkably successful in detecting compounds associated with prostate cancer in urine samples.
This headline is based on research that trained two explosive-detection sniffer dogs to identify the urine samples of men with prostate cancer. They then tested the dogs on urine samples from 332 men with the condition and 540 controls without the condition, most of whom were men.
One dog correctly identified all the samples from men with prostate cancer, and the other dog identified 98.6% of them. The dogs incorrectly identified between one and four percent of the control samples as being from men with prostate cancer ("false positives").
Some of the samples in the study were used for training the dogs and assessing their performance, and ideally the study would be repeated with entirely new samples to confirm the results.
This study suggests dogs can be trained to differentiate between urine samples from men known to have prostate cancer and people without the condition. But further testing should be carried out to test whether the dogs can accurately detect men with prostate cancer who are not yet known to have the disease.
It seems unlikely that dogs would be routinely used on a widespread basis to detect prostate cancer. If researchers can identify the exact chemical(s) the dogs are detecting in urine, they could try to develop methods to detect them.
Read more about potential warning signs for prostate cancer and when you should see your GP.
Where did the story come from?
The study was carried out by researchers from the Humanitas Clinical and Research Center and other centres in Italy. Sources of funding were not reported.
It was published in the peer-reviewed medical publication Journal of Urology on an open-access basis, so it is free to read online or download.
This study has been covered by a range of news outlets, no doubt owing to the appeal of any story involving dogs.
Most news sources illustrated the story with photos of the wrong breeds of dog, but The Independent got it right by showing a German Shepherd. The Daily Mirror suggested that the control group was all male, when this was not the case.
What kind of research was this?
This was a cross-sectional study that tested whether sniffer dogs could correctly differentiate between urine samples from men known to have or not have prostate cancer.
This type of study is suitable for an early-stage assessment of the promise of a new test. If successful, researchers would need to go on to test samples of men who are currently undergoing assessment for suspected prostate cancer, rather than those already known to have the disease. This would better assess how the dogs would perform in a real-world clinical situation.
The researchers say there is a need for a better way to detect prostate cancer. A blood test for prostate specific antigen (PSA) can indicate whether a man might have prostate cancer.
But PSA is also raised in non-cancerous conditions, such as infection or inflammation, so the test also picks up a lot of men who do not have the disease (false positives).
A raised PSA level alone is not a reliable test for prostate cancer. It needs to be combined with an examination and other invasive tests (for example, a biopsy) to determine whether a man has the condition.
Other studies have suggested sniffer dogs can detect the odour of certain chemicals in the urine of men with prostate cancer.
However, not all tests with dogs have been successful, possibly because of variations in how the dogs were trained and differences in the populations tested. The researchers wanted to test rigorously trained sniffer dogs to see how they would perform.
What did the research involve?
The researchers trained two sniffer dogs to identify urine samples from men with prostate cancer. They then allowed the dogs to sniff urine samples from men with or without prostate cancer and indicate which ones had the prostate cancer smell.
The urine samples were collected from 362 men with prostate cancer at different stages detected in various ways. The control samples were from 418 men and 122 women who were either healthy, or had a different type of cancer or another health problem.
The dogs taking part in the study were two three-year-old female German Shepherd explosive detection dogs called Zoe and Liu. They were trained using a standard procedure to identify prostate cancer samples using 200 urine samples from the cancer group and 230 from the control group.
In the first stages of training, urine samples from healthy women and women with other forms of cancer were used as the control samples to make certain there would be no chance of the sample being from a man with undetected prostate cancer. The next stages of training first used samples from young healthy men, and then older healthy men.
After the training, the researchers tested the dogs on all of the samples from the men with prostate cancer and controls in batches of six random samples. The researcher analysing the results did not know which samples were from men with prostate cancer.
What were the basic results?
One dog correctly identified all the prostate cancer urine samples and only incorrectly identified seven (1.3%) of the non-prostate cancer samples as coming from men with prostate cancer (false positives).
The other dog correctly identified 98.6% of the prostate cancer urine samples and missed the other 1.4% (five samples). She incorrectly identified 13 (3.6%) of the non-prostate cancer samples as coming from men with prostate cancer. The false positive results all came from men.
How did the researchers interpret the results?
The researchers concluded that a trained sniffer dog can identify chemicals specific to prostate cancer in urine with a high level of accuracy.
They say further studies are needed to investigate how well the dog sniffing test would perform in a real-world sample of men undergoing investigation for possible prostate cancer.
This study found highly trained sniffer dogs are capable of differentiating between urine samples from men known to have prostate cancer and people without the condition. The study's strengths are the rigorous training of the dogs and the large number of samples tested.
The samples tested were all from people already known to either have or not have prostate cancer, and included some samples used in the dogs' training. Ideally, the study would be repeated with completely new samples to confirm the results.
If the results are confirmed, the next step would be to test whether the dogs can accurately detect men with prostate cancer who are not yet known to have the disease. For example, the dogs could be used to assess the urine of men who have raised PSA levels but a negative biopsy who are being monitored to see if they develop the condition.
The researchers noted they could not completely rule out that a small number of men in the control group had undetected prostate cancer. The risk would be low as they were either young or had no family history of prostate cancer, no prostate enlargement detected on digital rectal examination, and low PSA levels.
It seems unlikely that dogs would ever be routinely used on a widespread basis to detect prostate cancer. However, if researchers can identify the exact chemical(s) the dogs are detecting in urine, they could try to develop methods of detecting these chemicals.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.