Can Dogs Detect Cancer?
With their strong sense of smell, our canine friends can do more than sniff out drugs.
With their strong sense of smell, our canine friends can do more than sniff out drugs. They may also smell cancer.
Cancer cells release certain odorous compounds into the urine or breath. Some dogs, especially those with proper training, can detect these compounds through their olfactory abilities.
There have been anecdotes from pet owners that their pets alerted them of their cancer. For example, some pet owners who were diagnosed with breast cancer described their pet as nuzzling into the owner’s breast and sniffing their breath prior to diagnosis.
There is also quite a bit of literature on canine olfactory detection of cancers such as prostate, breast, bladder, and lung. The table below summarizes a sample of studies on canine cancer detection. Scientists are studying this research to develop new methods for detecting cancer, such as electronic nose sensors.
Table. Examples of Studies on Canine Cancer Detection
Taverna et al. J Urol. 2015 Apr;193(4)
For dog 1, sensitivity was 100% (95% confidence interval [CI] 99.0-100.0) and specificity was 98.7% (95% CI 97.3-99.5). For dog 2, sensitivity was 98.6% (95% CI 96.8-99.6) and specificity was 97.6% (95% CI 95.9-98.7).
Elliker et al. BMC Urol. 2014 Feb 27;14:22
Three dogs reached training stage 2, and 2 of them learned to discriminate potentially familiar prostate cancer samples from controls. During double-blind tests using new samples, however, the 2 dogs did not indicate prostate cancer samples more frequently than expected by chance (dog A had sensitivity of 0.13 and specificity of 0.71; dog B sensitivity of 0.25 and specificity of 0.75). The other dogs did not progress past stage 1, as they did not have optimal temperaments for the sensitive odor discrimination training.
Ehmann et al. Eur Respir J. 2012 Mar;39(3)
Lung cancer was identified with an overall sensitivity of 71% and a specificity of 93%.
Sonoda et al. Gut. 2011 June; 60(6)
Breath and Watery Stools
The sensitivity of canine scent detection of breath samples compared with conventional diagnosis by colonoscopy was 0.91, and the specificity was 0.99. The sensitivity of canine scent detection of stool samples was 0.97 and the specificity was 0.99. The accuracy of canine scent detection was high even for early cancer.
Cornu et al. Eur Urol. 2011 Feb;59(2)
The dog correctly designated the cancer samples in 30 of 33 cases. Of the 3 cases wrongly classified as cancer, 1 patient was re-biopsied and a prostate cancer was diagnosed. The sensitivity and specificity were both 91%
McCulloch et al. Integr Cancer Ther. 2006 Mar;5(1)
Lung and breast
Overall sensitivity of canine scent detection compared to biopsy-confirmed conventional diagnosis was 0.99 (95% CI, 0.99, 1.00) and overall specificity 0.99 (95% CI, 0.96, 1.00). Among breast cancer patients and controls, sensitivity was 0.88 (95% CI, 0.75, 1.00) and specificity was 0.98 (95% CI, 0.90, 0.99)
Willis et al. BMJ. 2004 Sep 25;329(7468)
As a group, the dogs correctly selected urine from patients with bladder cancer on 22 of 54 occasions. This translated to a mean success rate of 41% (95% confidence intervals 23% to 58% under assumptions of normality, 26% to 52% using bootstrap methods), compared with 14% expected by chance alone.
Sensitivity refers to the probability of a positive test among patients with disease. Specificity refers to the probability of a negative test among patients without disease.
Proper dog training on detecting these cancer compounds is key. There does not appear to be a best dog breed, as a variety was used in these studies. The evidence is not conclusive at this time, and additional research is ongoing for various cancers.
While canines aren’t ready to replace conventional cancer screening tests just yet, cancer detection through their olfactory abilities does seem promising.