Dogs have been used for decades to assist the blind, find bombs, and sniff out drugs. It's no wonder they sniff out cancer. Radiological exams can be harmful to the body, so a dog that could sniff out cancer could be a huge asset. This article explains how they are training dogs to detect cancer cells in urine. I've seen dogs that could detect skin cancer by sniffing different parts of the body. I think it's amazing what you can train a dog to do.