Dogs cancer detection trials: how they work

Claire Guest founded the charity, Medical Detection Dogs (MDD) in 2008, and began working on the connection between dogs and humans for a range of medical purposes: to nudge sufferers of severe type 1 diabetes when their blood sugar is low; to alert Addison's patients of the onset of an attack; and to research if they can sniff out cancer cells.

Medical Detection Dogs are being officially trialled by the National Health Service (NHS) in the UK for their ability to sniff out even the earliest stages of the disease.

Their noses are so sensitive they are leagues ahead of any technology invented by man, said Guest.

The charity set up a training centre in Milton Keynes and supporters donated animals to take part in the detection trials – retired gun dogs, failed guide dogs ("the ones that get distracted by a smell and make their owners walk into a lamppost"), spaniels, labradors and other "inquisitive, happy little dogs".

The dogs work in a laboratory where tubes containing breath or urine samples are placed on a carousel.

They are trained, using a hand-held clicker (to reinforce correct behaviour), to stare intently at a sample they believe contains “abnormal” cells. They are then rewarded with a tennis ball or treat.

The part of the brain that controls smell is 40 times more powerful in dogs than humans, meaning they can detect odours at a concentration of one part per trillion.

Early studies, published in medical journals – The Lancet and British Medical Journal – have suggested dogs can detect bowel and lung cancer in breath samples. Both studies were preliminary and involved small numbers of patients.

Building on these studies, the charity launched breast-cancer trial, involving 1,500 patients at Buckinghamshire NHS Trust, which are now working to determine whether dogs can detect mutated cells from breath samples.