Dogs Detect Cancer in People

In 1989, a woman went to her dermatologist have a mole removed. She had become concerned because her dog, a Collie-Doberman mix, was constantly sniffing at it while ignoring her other moles, and had even tried to bite it off. The mole turned out to be cancerous, and early detection saved her life.

Nancy Best, another cancer survivor, asserts that she is alive today because of her dog Mia. Best had developed breast cancer in 2000 but didn’t know it. Her yellow Labrador suddenly became obsessed with her right breast, constantly sniffing at the spot and finally pressing down with her nose until Best found a lump. With early detection and treatment, Best recovered.

How do dogs detect cancer? Researchers don’t know for sure, but they theorize that because dogs have a far more powerful sense of smell than humans, they can detect the biomarkers given off by cancerous tumours.

Studies of Dogs’ Ability to Detect Cancer in Humans

In 2004, researchers at Amersham Hospital in Buckinghamshire, England, in collaboration with Hearing Dogs for Deaf People, set out to test what had always been suspected – that dogs have the ability to detect cancer in humans. They found that six dogs of various breeds were able to distinguish the urine of bladder cancer patients from that of healthy patients at a higher rate than chance alone. Interestingly, a person who had been categorized as healthy by pre-screening was identified as a cancer sufferer by all the canine sniffers. Further tests of the subject turned up a cancerous kidney tumour (Associated Press, 24 September 2004).

In 2006, the Pine Street Foundation, as part of an international collaboration, conducted a study using five dogs (three Labrador Retrievers and two Portuguese Water Dogs) volunteered by their owners (McCulloch et al., 2006). The breath of cancer patients and healthy controls was collected in tubes, which contained fiber to capture microscopic particles. The dogs were trained (using clickers, praise, and food rewards) to sit or lie down when they found a cancerous sample.

The dogs achieved a remarkable accuracy rate of 88% for breast cancer and 99% for lung cancer, much better than laboratory tests. Because the results of the study were so impressive, critics raised concerns about the possibility of a Clever Hans phenomenon. Clever Hans, a nineteenth-century horse, was purported to have mathematical abilities. Although Hans could give correct answers to math problems by tapping his hoof, it turned out that he was not a math prodigy. Rather, he was picking up on the subtle facial cues of his owner that told him when he’d reached the right number of taps. But those in the room with the dogs didn’t know which tubes held the cancerous samples, as the tubes had been collected and numbered elsewhere, so they couldn’t have inadvertently given anything away.

Other concerns raised included the possibility that dogs were simply picking up on other factors related to cancer, such as chemotherapy or smoking, but no chemotherapy patients were included in the study and there were smokers among both the cancer-afflicted and healthy human subjects. The results were also unaffected by other factors that might alter the breath samples, such as dental or sinus infections, or what subjects had recently eaten.

A more recent study conducted in Germany yielded similar results, with dogs correctly identifying 71% of lung cancer cases and 93% of cancer-free samples. Canine diagnostic accuracy was not affected by potentially confounding factors such as food odours, medications, tobacco smoke, or chronic obstructive pulmonary disease (Ehmann et al., 2011).

Early cancer warning could save lives and enable lower-toxicity treatments, and the results of this research suggest the possibility of creating new technologies for advanced chemical diagnostics. The Pine Street Foundation is not yet offering canine cancer screening to the public, however, as this method is not sufficiently advanced and more research is required. Visit the Pine Street Foundation for information about ongoing research.

Cats, Rats, and Other Animals May Also Be Able to Detect Cancer

According to Douglas (New Scientist, 2009), most cats have more scent receptors than the average dog (the exceptions being certain dog breeds such as Bloodhounds), and anecdotal evidence suggests that they can also detect cancer. In 2009, an orange tabby named Tiger suddenly developed the habit of climbing into bed with owner Lionel Adams and dragging his paw down Adams’ left side. Concerned about his cat’s strange behaviour, Adams’ went in for a check-up. Doctors found and removed a large tumour from his lung, a tumour which likely would have gone undetected for five or six months longer had the cat not taken action (United Press, 16 February 2009).

Tiger isn’t the only cat to detect metabolic changes related to human health. Oscar, resident cat of the Steere House Nursing & Rehabilitation Center in Rhode Island, has shown the ability to predict impending death with such accuracy that when Oscar snuggles up to a patient, staff actually alert the patient’s relatives.

Rats have also proven to be trainable for disease detection. Researchers in sub-Saharan Africa, where medical resources are limited, found that trained African giant pouched rats could detect tuberculosis in sputum samples with an accuracy rate of 72%-100% (Weetjens et al., 2009). This study suggests that sniffer rats could potentially replace the slower and more expensive screening methods currently used.

For more dog articles, see the main Dogs page.


    • Associated Press. (24 September 2004). “Study Shows Dogs Able to Smell Cancer.”
    • Douglas, K. (9 December 2009). “Dogs vs. Cats: The Great Pet Showdown.” New Scientist.
    • Ehmann, R.; Boedeker, E.; Friedrich, U.; Sagert, J.; Dippon, J.; Friedel, G.; & Walles, T. (2011). “Canine Scent Detection in the Diagnosis of Lung Cancer: Revisiting a Puzzling Phenomenon.” European Respiratory Journal, August 18, [Epub ahead of print].
    • Mann, J. (7 February 2006). “Cancer-Detecting Dogs.”
    • McCulloch, M.; Jezierski, T.; Broffman, M.; Hubbard, A.; Turner, K.; & Janecki, T. (2006). “Diagnostic Accuracy of Canine Scent Detection in Early- and Late-State Lung and Breast Cancers.” Integrative Cancer Therapies, 5(1).
    • McNeil, D.G. (17 January 2006). “Dogs Excel on Smell Test to Find Cancer.”
    • United Press International. (16 February 2009). “Cat Alerts Owner to Lung Cancer.”
    • Weetjens, B.J.; Machang’u, R.S.; Kazwala, R.; Mfinanga, G.; Lwilla, F.; Cox, C;, Jubitana, M.; Kanyangha, H.; Mtandu, R; Kahwa, A.; Mwessongo, J.; Makingi, G.; Mfaume, S.; Van Steenberge, J.; Beyene, N.W.; Billet, M.; & Verhagen. R. (2009). “African Pouched Rats for the Detection of Pulmonary Tuberculosis in Sputum Samples.” The International Journal of Tuberculosis and Lung Disease, 13(6): 737-743.

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