“Sniff, sniff!” “Is that Cancer?”


Source: Wikimedia Commons

Cancer sucks, it’s true.

But did you know, cancer stinks as well?

Someone asked me if cancer can affect our body odour. Well, yes.

Dogs, our furry friends with supernatural olfactory powers have demonstrated the ability to sniff out cancer, even during its early stages. Is there anything dogs can’t do?

So, how do they do it?

Cells require means for energy production and waste disposal to survive. This requires a complex series of chemical reactions called metabolic reactions (or metabolism) that can sometimes be intertwined in a web-like pattern.

Metabolism produces waste, molecules that are the products of careful processing by the cell (meticulous creatures, cells). Normally, the metabolic pathways in a cell are fixed, and for a normal population (of cells or people), they would be identical.

But because cancer is  weird, it likes to do stuff differently.

A characteristic of cancer cells is that they have altered metabolic pathways, that are sometimes beneficial for the cancer cell. For example, some cancer cells binge on glucose, because they process it in a different way, making the energy payoff extremely inefficient.

Okay, but how do they do it?

A widely accepted explanation is this: Because cancer cells have a weird metabolism, they produce metabolic waste that smells weird (to dogs, at least). And our friends with superpowers can (with some training) identify the funny smell of those little molecules that do not belong.

According to the website dogbreedinfo.com, compared to humans, the olfactory region of a dog’s brain is 40 times larger (that’s a lot!). This makes them much, much more sensitive to smell compared to us (estimates range from about 1,000 to 10,000,000 times more sensitive, depending on the breed). This helps them identify extremely faint odours, like those produced by the metabolic waste from cancer cells, or other biomarkers for various disorders.


A double-blind study published in the journal European Urology found that a Belgian Malinois shepherd could be trained to identify prostate cancer in patients by sniffing the odour of their urine. The dog (now my favourite superhero) could correctly identify prostate cancer in 30 of 33 cases (mind=blown).

Another study published in the journal Cancer Biomarkers, involving a group of four trained dogs, found that dogs could identify bladder cancer in urine samples with a sensitivity of up to 73%. This study also suggested the presence of volatile biomarkers in the urine, that help dogs identify cancer.

As if that wasn’t awesome enough, this study found that trained dogs could identify breast cancer and lung cancer with 88% and 99% accuracy, respectively. How? By sniffing the patient’s breath, of course! The study also showed that dogs could identify cancer during all 4 stages of the disease! If that isn’t amazing, I don’t know what is.

Coolest superpower ever, am I right?

Is this helpful?


A common non-invasive test for diagnosing prostate cancer is called the Prostate-Specific Antigen (PSA) test. It measures the amount of prostate-specific antigen (a protein produced by the prostate gland) in the serum, where a higher concentration of the protein usually correlates with the presence of cancer.

A review published in the Indian Journal of Surgical Oncology mentions the sensitivity of the PSA test to be 32% for detecting any prostate cancer and 68% for detecting high-grade cancers (sensitivities vary based on test parameters). When we compare this to the sensitivity of a sniff test (91%), we realise that using dogs as non-invasive means for preliminary diagnosis is a pretty good idea.

Also, consider cancers like bladder cancer, where invasive means of diagnosis are necessitated by a lack of non-invasive methods. The only non-invasive method for diagnosis of bladder cancer involves cytometry (a fancy word for cell counting), where cancer cells are manually counted in a blood or urine sample.  A simple sniff test, with a good enough sensitivity of 73% (as mentioned earlier) sounds like a great alternative.

Why aren’t we funding this?

Despite being a relatively new idea, disease detection (also called bio-detection) by dogs is gaining popularity. Apart from cancer, it has been reported that dogs can sniff out migrainesnarcolepsy, hypoglycaemia (fancy word for low blood sugar), seizures, etc. Dogs do this by recognising various volatile biomarkers.

Groups like Medical Detection Dogs and Assistance Dogs UK in the UK are actively involved in the promotion of dogs for assistance and diagnosis of medical conditions. There are many other international groups supporting bio-detection dogs and related research.

Dr Claire Guest, the founder of Medical Detection Dogs, discovered a lump in her left breast after her pet labrador kept nudging her breast with its nose. This led to an early confirmatory diagnosis, saving her life. She believes using dogs for early cancer diagnosis is a sure way to save lives. And I agree!

In conclusion, dogs are awesome.

UPDATE: Why aren’t we doing this, yet?

Because, the evidence, although promising, needs to be validated by means of critical evaluation by the scientific community. Some sceptics argue that present studies require precision. Volatile biomarkers need to be identified, and reliability of sniff tests needs to be assessed and compared against standard diagnostic methods.

P.S. While I do not suggest replacing traditional diagnostic methods with a sniff test, it might be useful to consider sniff tests as a preliminary test in diagnosing cancers.

And if you ever needed a reason to love dogs, you have one now.

Do you have a question about cancer? Leave it in the comments below.


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