Pet lovers have always suspected that man's best friend has a special ability to sense when something is wrong with us. Now, scientists have verified that dogs are able to smell cancer - sniffing out a case even doctors failed to find. Experts say it is unlikely pooches will become partners in cancer detection any time soon, but that the results of a study by British scientists are promising. They showed that when urine from bladder-cancer patients was set out among samples from healthy people or those with other diseases, the dogs - ordinary pets - were able to identify the cancer patients' urine almost three times more often than would be expected by chance alone. 'The issue is not whether or not they can detect cancer, because clearly they can. The issue is whether you can set up a system whereby they can communicate with you. That requires further ingenuity,' said Tim Cole, a professor of medical statistics at Imperial College in London, who was not connected with the research. The idea that they may be able to smell cancer was first put forward in 1989 by two London dermatologists, who described the case of a woman asking for a mole to be cut out of her leg because her dog would constantly sniff at it, but ignore all her other moles. One day, the dog tried to bite the mole off when the woman was wearing shorts. It turned out she had malignant melanoma - a deadly form of skin cancer. But it was caught early enough to save her life. A handful of anecdotes about dogs' cancer-sniffing abilities have previously been reported, but the latest study, published in a recent British Medical Journal, is the first rigorous test of the theory to be published. Researchers used urine from bladder-cancer patients, people sick with unrelated diseases and healthy people to train the dogs over seven months. In testing, the dogs correctly selected the right urine on 22 out of 54 occasions, giving an average success rate of 41 per cent. By chance alone, the expected rate would be 14 per cent. The two best dogs, Tangle and Biddy - both cocker spaniels - were right 56 per cent of the time, according to trainer Andrew Cook. They all did well, except for one, Toddy the mongrel. 'Toddy, bless him, was working at a rate no better than chance, really, but we still love him,' Mr Cook said. The most intriguing finding was in a comparison patient whose urine was used during training. All the dogs unequivocally identified that urine as a cancer case, even though screening tests before the experiment had shown no cancer. Doctors held more detailed tests and found a life-threatening tumour in the person's kidney.