I heard several times that dogs could detect cancer before it was detected by humans.

Can Dogs Smell Cancer?

There are many published studies that prove dogs can detect cancer through breath samples, and scientists and doctors are trying to come up with a breathalyzer test that works as good as the dogs nose. So far, the only ones that can smell cancer in early stages, are the dogs.

Is it true? If so, how can it be explained and which types of cancers are concerned? Can they sniff it directly on people, and not only on human secretions samples (urine, blood…)?

  • Because this isn't a sourced answer, I thought it was better suited as a comment. I have a bone disease in most of my joints. I've noticed when I'm in more pain, my cat will come and lay on the area that hurts, and purrs. It took me some time to realize that she senses I'm uncomfortable and comes over, then lays on the certain area because it's inflamed and much warmer than other parts of my body. This may be the reason that some animals can detect health problems in humans they're familiar with. Oct 22, 2014 at 21:35
  • You mean dogsdetectcancer.org says that dogs can detect cancer? You realize they get money if dogs CAN detect cancer. What's their bias going to be? MedScape or Mayo Clinic or the website of the ACS (cancer.org) might be better places to read about this.
    – geoO
    Feb 25, 2015 at 19:43

2 Answers 2


Dogs 'sniff out prostate cancer with 98% accuracy,' study finds

A new study from Italian researchers, presented at the 109th Annual Scientific Meeting of the American Urological Association in Orlando, FL, found that specially trained dogs were able to detect prostate cancer from urine samples with 98% accuracy.

For their study, the team wanted to see whether two highly trained dogs were able to detect prostate cancer-specific VOCs in the urine samples of 677 participants. Of these, 320 had prostate cancer ranging from low-risk to metastatic and 357 were healthy controls.

UAMS Researchers Use Scent-Trained Dogs to Detect Thyroid Cancer

The dogs were then presented with urine samples from patients — some with thyroid cancer and some with benign nodules — and asked to indicate whether each sample had thyroid cancer or not. Their results were compared to a surgical pathology diagnosis and matched in 30 of 34 cases, or 88.2 percent accuracy.

At least for some types of cancer it seems to work. The cancers make chemicals the body doesn't make naturally, the dogs can smell them. Since it's an area of ongoing research a list of what types is going to be subject to change.

  • Thanks for your answer Loren Pechtel, it is very interesting. Thus, I edited my question to know if there are also some studies about sniffing out cancer directly on people.
    – Einenlum
    Oct 21, 2014 at 20:04
  • I think the key phrase here is "specially-trained". That string, sans elaboration, makes me a tad skeptical. No offense meant :)
    – 299792458
    Oct 24, 2014 at 14:08
  • 2
    @New_new_newbie You let the dog sniff people with cancer and healthy people. The dog is rewarded for picking the one with cancer. Keep doing that until the dog is good at it, then let the dog smell people you want to test. It's just ordinary dog training. Oct 25, 2014 at 0:11
  • 1
    Plus the poster said "before detected by humans." In the study you cite the dogs were smelling samples KNOWN TO HUMANS to be cancerous or not. The dog didn't predict cancer that was later found.
    – geoO
    Feb 24, 2015 at 18:01
  • The first link goes to an uncritical media article that goes to a link that goes to a paywalled specious journal article from 2011. And the abstract presented there does not conclude anything but that further studies should be done. The second link is dead. And don't forget to read the studies that fail to show any dog cancer detection ability. Cherry picking is dishonest.
    – geoO
    Jan 29, 2018 at 14:37

There are quite a number of published studies showing that dogs can be trained to do this with high accuracy.

For examples:

  • Olfactory detection of prostate cancer by dogs sniffing urine: a step forward in early diagnosis

    The dog completed all the runs and correctly designated the cancer samples in 30 of 33 cases. Of the three cases wrongly classified as cancer, one patient was rebiopsied and a PCa was diagnosed. The sensitivity and specificity were both 91%.

  • Diagnostic accuracy of canine scent detection in early- and late-stage lung and breast cancers.

    Among lung cancer patients and controls, overall sensitivity of canine scent detection compared to biopsy-confirmed conventional diagnosis was 0.99 (95% confidence interval [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 0.98 (95% CI, 0.90, 0.99). Sensitivity and specificity were remarkably similar across all 4 stages of both diseases.

    Training was efficient and cancer identification was accurate; in a matter of weeks, ordinary household dogs with only basic behavioral "puppy training" were trained to accurately distinguish breath samples of lung and breast cancer patients from those of controls.

  • Olfactory system of highly trained dogs detects prostate cancer in urine samples.

    For dog 1 sensitivity was 100% (95% 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). When considering only men older than 45 years in the control group, dog 1 achieved 100% sensitivity and 98% specificity (95% CI 96-99.2), and dog 2 achieved 98.6% sensitivity (95% CI 96.8-99.6) and 96.4% specificity (95% CI 93.9-98.1). Analysis of false-positive cases revealed no consistent pattern in participant demographics or tumor characteristics.

  • Can dogs smell lung cancer? First study using exhaled breath and urine screening in unselected patients with suspected lung cancer.

    With an intensified training procedure, the exhaled breath and urine tests showed sensitivity rates of 56-76% and specificity rates of 8.3-33.3%, respectively, in our heterogeneous study population.

  • Following your links: dogs smelling VOC (that exist outside of a cancer setting), pilot work, "further studies are needed," "requires refinement." This would be laughable in a pre-med student's work. You also don't cite the scores of studies that fail to show any ability. You'd need to dig deeper than PubMed I'm afraid for those.
    – geoO
    Mar 2, 2015 at 1:28
  • Do any of you on Skeptics.SE really understand how proof or evidence works in a medical research setting and how many studies it takes to know what you are really talking about? If you had READ those studies (I did) you would have been too embarrassed to post them.
    – geoO
    Mar 2, 2015 at 1:29
  • Oddthinking, honestly, I know you read all of this. What is your level of skepticism? Aside from pop media stories and click-bait the evidence isn't there. I can't prove a negative so my answer was deleted as "semantic." My MD coworkers all laughed at this question and the un-skeptical answer that is accepted. Is this how you want skeptics.SE to be perceived? As an uncritical bubble where unfavorable answers are merely deleted instead of being held to vote?
    – geoO
    Mar 2, 2015 at 1:33
  • I have Oddthinking arguing for the answer above mine. And Sklivvz deleting my answer. How about giving the community a chance to read my answer? Do you think they are unable to make up their minds. Both of You: I CAN'T POST PROOF FOR A NEGATIVE! I CAN'T PROVIDE PROOF for a magical ability. The proof has to come from the answerer, and not a link to a blog post (this is medicine!)
    – geoO
    Mar 2, 2015 at 1:36
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    @jamesqf: It is better not to just post raw links, but to explain (ideally with an excerpted quote) what they conclude, and how they know it.
    – Oddthinking
    Mar 11, 2015 at 1:57

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