Breath

Background: While some research shows that dogs are able to detect lung cancer at above-chance levels using breath samples, the relative utility of other sample types has not been established. We evaluated the comparative utility of human breath and saliva samples for lung cancer detection using dogs. Methods: Seven dogs assessed breath and saliva samples from 154 patients attending a general respiratory clinic. Dogs were trained using an automated apparatus to identify samples from patients who were later diagnosed with lung cancer. Sensitivity and specificity measures were used to compare the dogs' performance with each sample type. Results: A mixed-methods logistic analysis of accurate responses to breath and saliva samples showed significantly higher detection of lung cancer-positive breath samples (mean 0.78, 95% CI 0.71-0.83) than of lung cancer-positive saliva samples (mean 0.42, 95% CI 0.34-0.50; p<0.001). There were no significant differences in accuracy of classification between non-target breath samples (mean 0.68, 95% CI 0.57-0.77) and non-target saliva samples (mean 0.68, 95% CI 0.56-0.77; p=0.854). Interpretation: The higher sensitivity of dogs to breath samples than to saliva samples suggests that breath samples have greater utility for canine scent detection of lung cancer. Although these findings support the continued use of breath samples for volatile-based lung cancer detection, with methodological improvements, saliva samples may also have utility for this purpose.