The first serious suggestion that dogs could "sniff out" cancer appeared in a letter to The Lancet in 1989.
From Dogs Can Smell Cancer - Secret Life of Dogs - BBC - YouTube: "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 tumors. They can even be taught to alert diabetics to low blood sugar levels."
BBC News - Medical Detection Dogs train animals to 'sniff out' breast cancer http://buff.ly/1mju3fG
SNIFFER DOGS IN THE MELANOMA CLINIC? : The Lancet http://buff.ly/1lFD0S9
Life With a Dog: You Meet People - NYTimes on health benefits of having a dog as a pet http://bit.ly/1e62kQq