Dogs can often detect cancer, even in its early stages, by smelling the breath of patients for telltale chemicals given off by cancer cells, a clinical trial in California shows.

The Portuguese water dogs and Labradors could, after brief training, sniff out which people had lung or breast cancer with accuracy rates between 88 and 99 per cent -- better than some laboratory tests.
http://www.canada.com/ottawacitizen/...1ca135&k=86741

I love dogs.