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A 2006 study stunned the scientific community when 5 ordinary pet dogs trained for just three weeks were able to accurately detect lung cancer 99 percent of the time. The dogs, who also achieved an 88 percent degree of accuracy (comparable to mammography) detecting breast cancer, were the focus of a study devised by the Pine Street Foundation, a private cancer research foundation based in San Anselmo, Ca.

The extraordinary ability of dogs, who have been shown to be able to distinguish certain chemicals diluted to a rate of one to a trillion, first came to light as a result of a case study in which a dog constantly sniffed a lesion on his owner. This lesion was found to be a malignant melanoma. That led to studies which showed dogs could detect bladder cancer in dried urine samples.

In this study, three Labradors and two Portuguese Water Dogs, (on loan from Guide Dogs for the Blind), successfully sussed out 55 cases of lung cancer and 31 cases of breast cancer using breath samples, differentiating them from the scents of 83 healthy control subjects. The dogs were clicker trained in the manner used to train bomb detection canines. They were cued to to sit when detecting a malignancy.

None of the test subjects had begun chemotherapy and smokers were included in both groups. Breath samples were collected in the same rooms on the same days. The only assistant who knew which breath samples came from cancer patients was out of the room whenever the dogs were working.

In 2007, Pine Street Foundation began chemical analysis on collected breath samples to try to figure out what the dogs are cueing on. Plans are underway to launch a study which should show whether the dogs will be useful in diagnosing early stage ovarian cancer.