Dogs have a very sensitive sense of smell which humans have put to use by training them to sniff out explosives and narcotics.
This remarkable sense of smell can also be useful in the medical world, as dogs are able to sniff out and detect viruses, bacteria, and certain diseases, including cancer in a person’s skin, urine, and sweat.
Like many other diseases, cancers leave specific traces, or odour signatures, in a person’s body and bodily secretions. Cancer cells, or healthy cells affected by cancer, produce and release these odour signatures. Depending on the type of cancer, dogs are able to detect these signatures in a person’s skin, breath, urine,faeces, and sweat, and can, with training, alert people to their presence.
These dogs that undergo training to detect certain diseases are referred to as medical detection dogs – they can detect some substances in very low concentrations, e.g. parts per trillion, which makes their noses sensitive enough to detect cancer markers in a person’s breath, urine, and blood.
Which Types of Cancer can a Dog Smell?
Research has shown that dogs can detect many types of cancer. For example, a case study published in BMJ Case Reports describes how a 75-year-old man visited a doctor after his dog licked persistently at a lesion behind the man’s ear. The doctor performed diagnostic tests and confirmed malignant melanoma.
While nobody had trained this person’s dog to specifically detect cancer, most research studies into canine cancer detection involve teaching individual dogs to sniff out specific cancers.
Trained dogs are able to detect colorectal cancer from people’s breath and watery stool with high levels of accuracy, even for early stage cancers. The presence of gut inflammation or non-cancerous colorectal disease does not seem to affect dogs’ ability to detect these cancers.
Dogs can also detect lung cancer from a person’s breath. One study found that a trained dog had a very high rate of accuracy in distinguishing between the breath of people with and without lung cancer.
They are also able to detect ovarian cancer from blood samples and prostate cancer from sniffing a person’s urine.
One study found that dogs trained only to detect breast cancer were also able to detect melanoma and lung cancer, meaning that there may be a common odor signature across different types of cancer.
Are Dogs used in Cancer Research and Diagnosis?
The fact that dogs can detect cancer has significant benefits for humans as it is a low-risk, noninvasive method.
Medical detection dogs present few side effects and may offer advantages because they are mobile, can begin work quickly, and can trace an odour to its source. They also have the potential for use in patient-care settings or laboratories to identify cancer in tissue samples from people with suspected cancers.
Dogs’ abilities may also help with developing machines that can reliably detect odour signatures from cancer, such as electronic noses.
However, research is still underway and the effectiveness and reliability of canine cancer detection requires further research.