At present lung and breast cancers are the leading causes of cancer deaths worldwide, and early detection of the disease is of paramount importance.
In this new study researchers reveal scientific evidence that a dog's extraordinary scenting ability can distinguish people with both early and late stage lung and breast cancers from healthy controls.
The research, which was carried out in California, was recently filmed by the BBC in the UK, and is about to be broadcast in the U.S.
Previous scientific studies have shown the abilities of dogs to identify chemicals that are diluted as low as parts per trillion, but the clinical implications first came to light in the report of a dog alerting its owner to the presence of a melanoma by constantly sniffing the skin lesion.
Studies published in accredited medical journals have confirmed this ability of trained dogs to detect both melanomas and bladder cancers.
But the new study, led by Michael McCulloch of the Pine Street Foundation in San Anselmo, California, and Tadeusz Jezierski of the Polish Academy of Sciences, Institute of Genetics and Animal Breeding, is the first to test whether dogs can detect cancers only by sniffing the exhaled breath of cancer patients.
For the study, five household dogs were trained within a short 3-week period to detect lung or breast cancer by sniffing the breath of cancer participants.
The trial itself included 86 cancer patients, 55 with lung cancer and 31 with breast cancer, and a control sample of 83 healthy patients.
All the cancer patients had recently been diagnosed with cancer through biopsy-confirmed conventional methods such as a mammogram, or CAT scan and had not received any chemotherapy treatment.
The dogs were presented with breath samples from the cancer patients and the controls, which were captured in a special tube.
They were trained to give a positive identification of a cancer patient by sitting or lying down directly in front of a test station containing a cancer patient sample, while ignoring control samples.
In the experiment standard, humane methods of dog training using food rewards and a clicker, as well as assessment of the dog's behavior by observers blinded to the identity of the cancer patient and control samples, were deployed.
The study showed that the dogs were able to detect breast and lung cancer with sensitivity and specificity between 88% and 97%, and it appears that this high accuracy persisted even after results were adjusted to take into account whether the lung cancer patients were currently smokers.
The study also confirmed that the trained dogs were even able to detect the early stages of lung cancer along with early breast cancer.
The researchers conclude that breath analysis has the potential to provide a substantial reduction in the uncertainty currently seen in cancer diagnosis, but further work is needed in order to standardise and expand the methodology.
The research will be published in the March 2006 issue of the journal Integrative Cancer Therapies.