Dogs have an acute sense of smell. Researchers are finding that dogs can sniff out cancer by detecting the odor signatures of breast, colorectal, lung, and other types of cancer. More investigation into canine cancer detection is necessary.

Humans have put dogs’ remarkable sense of smell to use by training them to sniff out explosives and narcotics. Their powerful noses can also detect viruses, bacteria, and signs of cancer in a person’s body or bodily fluids.

In this article, we look at the evidence behind dogs’ abilities to smell and identify different types of cancer, and how medical professionals can use dogs to help diagnose the condition.

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Simon King, CC BY-SA 4.0 via Wikimedia Commons

Research suggests that dogs can detect many types of cancers in humans.

Like many other diseases, cancers leave specific traces, or odor signatures, in a person’s body and bodily secretions. Cancer cells, or healthy cells affected by cancer, produce and release these odor signatures. They detect these odors in substances called volatile organic compounds (VOCs).

Depending on the type of cancer, dogs are able to detect VOCs in a person’s:

  • skin
  • breath
  • urine
  • feces
  • sweat

Dogs can detect these odor signatures and, with training, alert people to their presence. People refer to dogs that undergo training to detect certain diseases as medical detection dogs.

Trained dogs can detect some substances in very low concentrations, as low as parts per trillion, which makes their noses sensitive enough to detect cancer markers in a person’s breath, urine, and blood.

Research has shown that dogs can detect many types of cancer, such as:

For example, one case report describes how a 75-year-old man visited a doctor after his dog licked persistently at a lesion behind the man’s ear.

The doctor performed diagnostic tests and confirmed malignant melanoma.

Nobody had trained this person’s dog specifically to detect cancer. However, most research studies into canine cancer detection involve teaching individual dogs to sniff out specific cancers.

Scientists have found evidence that some dogs can detect colorectal cancer from people’s breath and watery stool with high levels of accuracy, even for early-stage cancers. The presence of gut inflammation or noncancerous colorectal disease does not seem to affect dogs’ ability to detect these cancers.

Dogs may also detect lung cancer from a person’s breath. One study found that a trained dog had a very high rate of accuracy in distinguishing between the breath of people with and without lung cancer.

In another study, two dogs received training for 1 year. After this, researchers presented the dogs with a number of urine samples. The dogs proved 45–73% accurate in detecting lung cancer through the samples.

Dogs have also detected ovarian cancer from blood samples and prostate cancer by sniffing a person’s urine.

In 2021, researchers reported that a dog trained to detect signs of breast cancer in urine was able to detect breast cancer with 100% accuracy among urine samples from 200 people. Of these, 40 had breast cancer, 182 had other cancers, and 18 had no cancer. This study has yet to be repeated with a larger population of dogs to see if the outcomes can be reproduced.

One study found that dogs trained only to detect breast cancer were also able to detect melanoma and lung cancer. This suggests there may be a common odor signature across different types of cancer.

The fact that trained dogs can detect cancer may have significant benefits for humans. Using dogs to support the detection and diagnosis of cancer is a low-risk, noninvasive method.

Medical detection dogs present few side effects and may offer advantages because they are mobile, can begin work quickly, and can trace an odor to its source.

They also have the potential for use in patient care settings or laboratories to identify cancer in tissue samples from people with suspected cancers.

Dogs’ abilities may also help with developing machines that can reliably detect odor signatures from cancer, such as electronic noses.

However, research is still underway and the effectiveness and reliability of canine cancer detection requires further investigation. Other areas for research include which breeds of dogs are most suited to detection and which kind of training will be most effective.

Dogs have a highly developed sense of smell, and some can detect the odor signatures of various types of cancer. Dogs have also shown they can detect colon cancer, prostate cancer, breast cancer, and melanoma by sniffing people’s skin, bodily fluids, or breath.

Researchers are currently exploring the possibility of using specially trained medical detection dogs in diagnosing and tracking cancer.

Canine cancer detection is a simple, noninvasive procedure with potentially fewer side effects for people. However, further investigation is necessary to validate this method for use in clinical practice.