Medical dogs can sniff out number of diseases from Parkinson's disease, cancers, to malaria. As cancer tumours release elevated volatile organic compounds, dogs can be trained to identify them. A dog's sense of smell is remarkable and they are able to detect stable concentration thresholds of 1-2 parts per trillion, that's the equivalent of one teaspoon of sugar in two Olympic-sized swimming pools of water.

"Compared to humans, who have five million scent receptors, dogs can have up to 300 million. Where we might think 'that casserole smells nice', dogs can layer scents, so in the casserole they can smell the meat, the onion, the cabbage, the tomatoes," Mrs Blomfield, the dog trainer explains. Dogs can detect prostate cancer cells in urine. Currently there are limitations concerning blood test result for prostate cancer. And digital rectal exams are not popular. Hence the vision of men having to only provide a non invasive urine sample to be tested by dog is ideal.

Medical Express, Good boy! New Zealand researchers using dogs to sniff out prostate cancer, March 5, 2019 by University of Otago.

https://medicalxpress.com/news/2019-03-good-boy-zealand-dogs-prostate.html