A DOG has been credited with saving her owner's life after her unusual behaviour alerted him to undiscovered lung cancer.

Sassy was training to be a guide dog with puppy walker David Eyre when she suddenly started climbing on his knee and putting her head on his chest - something she had been taught not do as part of her training.

But she continued with the behaviour and it prompted David, who had previously had leukaemia, to go to the doctor and then for a scan where lung cancer was diagnosed. David, 75, and his wife, Hazel, of Cemetery Road, Wombwell, started puppy walking for Guide Dogs for the Blind after he recovered from leukaemia.

The couple has assumed that blackouts which David started experiencing last year were related to his treatment for the disease, which left him with just a third of a heart. David said as part of her guide dog training Sassy had been taught not to jump up, so was surprised when she started to climb up and rest her paws and head on his chest.

Her unusual behaviour helped convince the couple something was wrong and after a visit to the hospital, David was diagnosed with lung cancer in his right lung - right where Sassy had been placing her head.

"There was a dark spot on the x-ray right around where Sassy had placed her head," he said. "I've now been for 20-plus treatments of radiotherapy and while it hasn't shifted it, it has stopped it growing."

While he was having his treatment Sassy joined David on his visits to Sheffield's Weston Park hospital for treatment. Hazel said: "She would walk into the ward off her lead, trot up and put her chin on the knee of two or three different people. They were all saying how lovely she was, but I daren't say that it was because she knew they were poorly.

"She never barks she just grumbles, but she kept grumbling."

The two-year-old Labrador was the seventh guide dog David and Hazel had trained, but ironically the dog's own health problems quickly meant Sassy failed to pass the test to become a guide dog and the couple were offered the chance to have her back, deciding to buy her to keep as a pet. Like David, Sassy is now on a heavy prescription of medication to battle her various health problem.

Charity Medical Detection Dogs is working on the forefront of research into how dogs can help identify cancer early through their sense of smell. CEO and co-founder Claire Guest said: "David's story adds to a growing collection of anecdotal evidence that dogs are able to detect the smell of cancer.

"Medical Detection Dogs trains dogs to detect the odour of human disease, such as cancer, in urine and swab samples. Our dogs never come into contact with patients, but work in a specially designed bio detection area at our centre near Milton Keynes.

"In training trials, our dogs have achieved a reliability as high as 93 per cent. That's much more reliable than most existing tests. We are now working with the NHS on major trials to show that harnessing dogs' extraordinary olfactory powers has the potential to save thousands of lives."