Originally posted by Jeff Lebowski
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Fittingly, I listened to this while walking my dogs. One of them would stop dead in her tracks to sniff my other dog's favorite pee rock, even a couple of weeks after he died. So you don't have to convince me of their olfactory excellence. And I really appreciated Gladwell's easy to understand discussion about sensitivity/specificity and negative/positive predictive values, without using those terms and getting bogged down in definitions.
I skimmed over the two most interesting articles he brought up, about prostate and colon cancers. Up front, he did oversell just how good dog sniffing was for these. For prostate cancer, the study used urine from men who had very high-grade cancer. It is safe to assume that these cancers are more extensive and of a higher stage than the more common prostate cancers, which would make sense if the tumor is developed enough to cause a detectable scent. But even for these cancers, the dog sniffing results were "71% sensitive and between 70–76% specific at detecting Gleason 9 prostate cancer".
The colon cancer paper was better designed. It included a bunch of non-cancer patients with colonic disease other than cancer, which conceivably could cause a detectable odor. And based on the paper, dogs were good at detecting the cancer patients via exhaled breath and poop smelling. The results were around 91-97% sensitivity and 99% specificity for both breath and stool samples, when compared to colonoscopy. That is pretty interesting, though I couldn't find the characteristics such as cancer stage of the cancer patients, which really does raise eyebrows. But still, it proves the point that cancer causes a detectable odor.
Having said this, colonoscopy serves a purpose other than just diagnosing cancer. It documents and removes pre-cancers, which according to that paper dogs couldn't detect. Also, the paper is from 2011. In the 15 years since fecal occult blood testing has progressed to DNA testing which has similar sensitivity and specificity to colonoscopy in many patients. It would be interesting to compare DNA-based tests with canine olfactory detection.
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