Photograph by Emma Jeffery
The scientific basis of the ability of dogs to detect the odour of cancer is believed to be linked to Volatile Organic Compounds produced by malignant cells. It has been established that during tumor growth protein changes in these cells which leads to peroxidation of the cell membrane components and this produces Volatiles that can be detected in the headspace of the cells.
Following our 2004 BMJ study, Medical Detection Dogs (aka Cancer and Bio-detection Dogs) has continued this work and recently published in the journal Cancer Biomark, Willis CM, Britton LE, Harris R, Wallace J, Guest CM. ‘Volatile organic compounds as biomarkers of bladder cancer: sensitivity and specificity using trained sniffer dogs’.
A recent study has just completed by Cornu et al, ‘Olfactory Detection of Prostate Cancer by Dogs Sniffing Urine: A Step Forward in Early Diagnosis’, indicated the possibilities of this. A second study in 2011 by Senoda on colorectal cancer using faecal samples (sensitivity 0.97 specificy 0.99) published in the journal Gut has shown equally promising results.
In 2011 the charity published in the journal ‘Cancer Biomark’ ‘Volatile organic compounds as biomarkers of bladder cancer: Sensitivity and specificity using trained sniffer dogs’. Specificity ranged from 92% for urine samples obtained from healthy, young volunteers down to 56% for those taken from older patients with non-cancerous urological disease.
There is strong indication from a number of studies that cancer Volatiles may appear on the breath at an early stage in the disease process.
Additional evidence published in the European Respiratory Journal carried out in Schillerhoehe Hospital Germany. This is the first to be published showing that sniffer dogs can reliably detect lung cancer from a breath sample.
The Odoreader® from Bristol Urological Institute and Liverpool University is a direct result of the BMJ paper in 2004
and is able to help detect and diagnose early stage bladder cancer.
This work opens the door of Volatile Organic Compound detection for cancer diagnosis and suggests that the conditioned dog should be used in the near future to validate candidate molecules emerging from metabolomic screening. Evidence based building indicates that dogs could assist in improving current diagnosis of a significant number of cancers.
How do we determine accuracy?
Below are graphs of the correct detection of bladder cancer by Cancer Detection Dog Daisy.
Fig 1 Sensitivity: 93% of +ve samples correctly indicated
Sensitivity relates to the test's ability to identify positive results. The sensitivity of a test is the proportion of samples that are known to have the disease.
In Fig 1 Orange is the correctly identified positive cancer sample – blue is the correctly identified normal sample.
Fig 2 Specificity: 95% of -ve samples correctly ignored
Specificity relates to the test's ability to identify negative results. The specificity of a test is defined as the proportion of samples that are known not to have the disease.
In Fig 2 Orange is correct ignore – blue is picked in error.
What are the dogs detecting?
Dogs with their incredible sense of smell can detect the minute odours now understood to be associated with many cancers. As yet we do not know exactly what it is the dogs can smell because they cannot tell us what markers they are sensing.
What is our aim?
Our primary purpose is to enable the development of more electronic systems using the information that we have gained from the dogs.