Canine and electronic noses and their medical applications

A sniffer dog has proved successful at detecting thyroid cancer in undiagnosed patients, according to recent reports from the US. It was 88% successful at detecting tumours from urine samples.

This is not a completely new concept however, as the first serious suggestion that dogs could ‘sniff out’ cancer appeared in a letter to The Lancet in 1989. Subsequent studies have suggested that dogs can also detect cancer of the bladder, lung, bowel and breast.

It is thought that dogs’ noses, which contain around 40 times more olfactory receptors than humans’, can detect volatile organic compounds produced by malignant cells. During tumour growth, changes in some cellular proteins lead to peroxidation of cell membrane components which produces volatile organic compounds that can be detected in the headspace of cells. These cancer volatiles are excreted in urine or exhaled on the breath at an early stage of the disease.

Prototype ‘electronic noses’ have been developed using nanotechnology in the hope of creating a more practical screening tool. The Na-Nose, for example, can detect lung cancer from exhaled breath with up to 95% accuracy. The device analyses over 1,000 different gases in the breath by binding gases to specific nanomaterials in a technique known as volatile organic compound detection. Developers hope that GPs will eventually have a pocket-sized Na-Nose in their surgeries, and even that it could be incorporated into a mobile phone app.

The Odoreader is a prototype device that can diagnose bladder cancer from urine samples. It analyses the gas emitted from urine and produces a chemical profile that can determine the presence of cancer cells in the bladder. Researchers are also using the Odoreader to detect differences in odours from the urine of men with prostate cancer.

Researchers at the University of Leicester have used an electronic nose to detect different strains of Clostridium difficile in faeces. They showed that different levels of methanol, sulphur compounds and other gases were produced by the 10 different strains analysed. The device uses a mass spectrometer to determine strain information, which would allow treatment to be tailored.

While dogs’ noses may not be a practical tool for use in clinical environments, their excellent sense of smell is being used to warn patients of pending medical emergencies within their own homes. The Medical Detection Dogs charity provides bio-alert dogs for patients with diabetes, Addisonian crisis, seizures, severe allergies and narcolepsy.