Of all animals, so far, the evidence shows that dogs are the best to detect early stage cancer in humans. Canine cancer detection is an approach to cancer screening that relies upon the olfactory ability of dogs to detect very low concentrations of the alkanes and aromatic compounds generated by tumors.
One of these aromatic compounds that Tumors generate is the gaseous sulfur-containing molecule that trained diagnostic dogs can detect at a very high success rate. (Source)
In terms of the types of sniffable cancers, there are skin cancer sniffing dogs (Source) as well as breath-sniffing dogs that can pickout people with lung cancer. (Source). Dogs have been repeatedly able to detect lung cancer from a person’s breath with high rate of accuracy. (Source)
Dogs can also detect bladder cancer in urine (Cf pee-sniffing dogs, Source) and gas-fart-sniffing canines for colorectal cancer. (Source) Trained dogs are also able to detect colorectal cancer from people’s breath and watery stool with high levels of accuracy, even for early stage cancers.
A case study published in BMJ Case Reports 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.
Dogs are also able to detect ovarian cancer from blood samples and prostate cancer from sniffing a person’s urine. One study found that dogs trained only to detect breast cancer were also able to detect melanoma and lung cancer, meaning that there may be a common odor signature across different types of cancer.
Mechanisms: Transfer of Survival Information
The presence of gut inflammation or noncancerous colorectal disease does not seem to affect dogs’ ability to detect these cancers. In reality, inflammation and a strong immune response are key pathways with regard to smell detection. Previous research conducted by Monell researchers in mice has shown that even inflammation can change an individual’s bodily odor. These subtle changes allow the rodents to pick up cues about possible signs of infection and thus steer clear of contagion. This is a remarkable transfer of information via olfaction that specifically alters physiology and could play a role in disease transfer among individuals in many species.”
From an evolutionary standpoint, being able to sniff out a sick individual would be an advantage. If a mouse could detect the whiff of an immune response and avoid a colleague with an onboard pathogen, their ability to survive would be enhanced. This is not just idle theory; it is now well established that rodents can avoid sick individuals through odor detection alone.
Humans also appear to be able to sniff out those who are currently embarking on an immune response, and a study published in the journal Psychological Science put this hypothesis to the test. First, samples of body odor were taken from a group of healthy volunteers. Then, the scientists triggered an immune response by injecting the participants with endotoxin. Their body odor was once again sampled, and then assessed and rated. Within just a few hours, endotoxin-exposed individuals had a more aversive body odor relative to when they were exposed to a placebo. Moreover, this effect was statistically mediated by the individuals’ level of immune activation. Therefore, sick people smelled worse – and the sicker they were, the worse their smell was rated. The differences in odor could be detected within just 4 hours of the immune system being triggered. It is also worth noting that the sick people did not sweat more, and that the smell was not only stronger, but different, as well.
In humans, body odor is primarily due to bacteria and skin gland secretions, particularly the apocrine sweat glands that are found in the armpits, among other locations. Body odor is, in fact, a complex and variable cocktail of compounds. The main components of human axillary odor are unsaturated or hydroxylated branched fatty acid swith E-3M2H (E-3-methylhex-2-enoic acid) and HMHA (3-hydroxy-3-methylhexanoic acid), sulfanylalkanols and particularly 3M3SH (3-methyl-3-sulfanylhexan-1-ol), and the odoriferous steroids androstenone (5α-androst-16-en-3-one) and androstenol (5α-androst-16-en-3α-ol). (Source) E-3M2H is bound and carried by two apocrine secretion odor-binding proteins, ASOB1 and ASOB2, to the skin surface. (Source)
There are a number of ways that an infection could modify a person’s aroma. Firstly, human bodies are rammed to the rafters with microbes, some of which play a role in the way we smell. Therefore, a pathogen that alters the levels or types of these microbes could also adjust to body odor. Secondly, genes associated with the major histocompatibility complex that control the body’s immune response also influence odor and mating preferences in mice. Thirdly, an activated immune system changes the excretion of other metabolic byproducts from the endocrine, or hormonal, system. For instance, levels of corticosterone in the blood are elevated during an immune response, and androgens are reduced.
VOCs as Cancer Biomarkers ?
Just like the smell of rotten apples from one’s breath is a sign of diabetes, putrefaction is a sign of cancer ..
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At the ACR Institute, we are working in getting at least one dog or cat that can be trained in this skill.
For more evidence on this question, see Source.
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