In an ongoing study in England, researchers are training a handful of dogs to identify the urine samples of patients with cancer. In a 2004 study, they correctly detected bladder cancer 22 times out of 54 tries.
Carol Witcher has been free of cancer for two years. "I had rescued him when he was about seven months old," she said of Floyd Henry. "He, in turn, rescued me."
ABC News' Katie Moisse and Courtney Hutchison contributed to this story.