This is Max the dog and his human Maureen. An amazing BBC Earth report tells their story: Max became depressed when he started to smell the cancer that Maureen was developing inside her breast. It's a really incredible tale.
According to BBC Earth's Secret Life of Dogs, "dogs watch us all the time and read our body language like a sixth sense. They also smell our bodies for changes. Max smelt cancer in Maureen before any medical scans could pick it up. Dogs do this naturally and can be trained to pick up on tiny volatile chemicals given off by cancerous tumours. They can even be taught to alert diabetics to low blood sugar levels." [Thanks Anna Jane!]