Specially trained dogs can reliably detect lung cancer in most patients by sniffing their breath, data indicate.

Dogs successfully identified 71 patients out of 100 with biopsy-confirmed lung cancer from breath samples, reported Thorsten Walles, MD, of Schillerhoehe Hospital in Gerlingen, Germany, and colleagues online in the European Respiratory Journal.

The researchers found that among another 400 samples from patients with lung cancer, the sniff test resulted in just 28 false positives.

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These findings confirm that a stable set of lung-cancer specific volatile organic compounds (VOCs) exists and could be used as a marker for the disease that is detected in the future by more conventional means.

“This is a big step forward in the diagnosis of lung cancer, but we still need to precisely identify the compounds observed in the exhaled breath of patients,” Walles said in a press release.

This is not the first time that dogs have been touted for their cancer-detecting ability. In a case report from 1989, a man’s melanoma was diagnosed after his dog would not stop sniffing his skin lesion, and several earlier studies have found that dogs are able to identify cancer in the breast and colon.

The further investigate this association, Walles and colleagues had dog trainers teach two German shepherds, one Labrador retriever, and one Australian shepherd to lay down in front of test tubes containing exhalations from 35 lung cancer patients and 60 healthy controls.

The testing involved 50 healthy people, 25 patients with histologically confirmed lung cancer, and 50 patients with chronic obstructive pulmonary disorder (COPD), who were different from the patients used in the training phase to ensure that the dogs were not accustomed to the participants’ characteristic odors.

There were three testing phases. In the first, the dogs differentiated between healthy participants and those with lung cancer. Surprisingly, this test proved most difficult, with 22 correct results vs. 18 false results.

The dogs were more successful in the second phase, correctly identifying 32 patients with lung cancer and COPD with just eight false results.

In the third phase, the dogs were required to detect patients with lung cancer from all three groups. They correctly identified 19 patients with lung cancer, and had only one false result.

The overall sensitivity of the sniff tests was 71% and specificity was 93%, according to the researchers (95% CIs not reported), and varied little according to disease stage. Accuracy according to cancer stage was as follows:

  • 75% among two patients with stage IIa tumors and two patients with IIb tumors
  • 94% among four patients with stage IIIa disease
  • 75% among five patients with stage IIIb disease
  • 63% among 11 patients with stage IV disease

The dogs were also able to accurately differentiate between smokers and nonsmokers, indicating that they were not just simply responding to tobacco related breath components.

Although the findings are promising, scientists will not be able to develop a reliable screening test based on the dogs’ abilities without better understanding what, specifically, they are responding to, the researchers emphasized.

“It is unfortunate that dogs cannot communicate the biochemistry of the scent of cancer,” Walles said.

Ehmann R et al. Eur Resp Journal. 2011; doi:10.1183/09031936.00051711.