These research results do not surprise many pet owners. A dog named Trudi kept sniffing her owner's leg. The owner went to the doctor, who found that the man had melanoma. This is a form of skin cancer that can be deadly. The dog identified it early, before it spread. Another patient was treated for cancer, but her dog kept sniffing and marking noises at the cancer site. The doctor had not removed all the cancer. Once again, a dog identified its owner's cancer.