Dogs' keen sense of smell might help in the early diagnosis of cancer, researchers report in the current issue of Integrative Cancer Therapies. The findings show that trained ordinary household dogs can detect early-stage lung and breast cancers by merely sniffing the breath samples of patients.
"We've seen anecdotal evidence before suggesting that dogs can smell the presence of certain types of cancer," Michael McCulloch, from the Pine Street Foundation in San Anselmo, California, told Reuters Health, "but until now, nobody had conducted a thorough study such as this." Researchers have observed that cancer cells release molecules different from those of their healthy counterparts, and that might be perceived by smell by the highly sensitive dog's nose.
For the study, five dogs, three Labrador retrievers and two Portuguese water dogs, were trained by a professional instructor to respond differently to exhaled breath samples of healthy and cancer patients. "The dogs learned to sit or lie down in front of cancer patient samples and to ignore control samples through the method of food reward," McCulloch explained.
After an extensive, though relatively short, period of training, the McCulloch and his colleagues tested the animals' ability to distinguish cancer patients from controls. The animals were given breath samples from 55 patients with lung cancer, 31 with breast cancer and 83 healthy controls who were not included in the original training sessions. Neither the dogs nor the observers knew the identity of the samples.
McCulloch's group found that the dogs were able to correctly distinguish the breath samples of cancer patients from the those of the control subjects in about 90 percent of the cases, even after the researchers adjusted the results to take into account whether the lung cancer patients were smokers. The dogs were also capable of detecting early-stage lung and breast cancers.
"These results show that there is hope for early detection," McCulloch said. The researchers are planning to conduct further studies on the breath composition of cancer patients to possibly design an electronic device that can do the dogs' job. "I hope people will be interested in pursuing this research," McCulloch added. "It shows that there is definitely something out there."