You’ve heard of drug-sniffing dogs and bomb-sniffing dogs. Meet the latest canine nose specialty: cancer-sniffing dogs.

It began after a few dog owners alerted their doctors to the notion that their pooch suddenly and relentlessly started sniffing at a mole or small mark on their arm or leg. The dogs would whimper, scratch and bite at the offending area. In all cases, the owners were diagnosed with a malignant melanoma, or skin cancer, which is highly curable when detected early. These anecdotes were striking enough to be written up in several medical journals.

More thorough studies have been conducted in recent years. When it comes to sniff power, dogs can identify chemical traces in the range of parts per trillion. Cancer cells emit different metabolic waste products than normal cells, and in the case of breast and lung cancer, those waste products are exhaled by the patient. A dog’s keen sense of smell can notice that strange biochemical marker in his owner’s breath, even when the disease is in the very early stages. Further testing with dogs identifying the urine of prostate cancer patients is also looking hopeful.

Scientists are trying to mechanically duplicate the canine sniffer, and hope to someday soon develop an “electronic nose” which would probably end up in an oncologist’s office long before a Labrador retriever would.