Cancer-detecting dogs

Source: Paul167, Wikimedia Commons

 

People have attributed healing properties to pets for centuries. Some have even claimed that their pet can tell when they are sick, with training organizations over the past few years claiming that they can train dogs to detect cancer. But can dogs really smell cancer? One small study says that they probably can and found that they may be successful at decreasing the false positive rate of current methods used in prostate cancer screening.

A dog’s sense of smell is a thousand times more sensitive to odor molecules than the human sense of smell. Each dog nose has 220 million olfactory receptors (compared to a human’s mere 5 million). This incredible sense of smell has made dogs famous for sniffing out what humans want. But what if what the human wants is a diagnosis?

Current prostate cancer screening involves screening for prostate-specific antigen (PSA) in the blood. The problem is that the test is not sensitive enough to tell the difference between normal age-related growth of the prostate (sometimes in the form of benign tumors) and malignant cancers. Another test is considered more invasive, and involves the doctor feeling around inside the patient’s rectum to examine the prostate. Most men have a similar basic prostate exam at their regular physicals once they are over the age of 40. This exam can catch an enlargement of the prostate, but may miss small, aggressive tumors. Current screening methods are somewhat controversial because they sometimes lead to increased anxiety over false positives and unnecessary medical procedures with side effects that can negatively the man’s quality of life for harmless changes in the prostate gland.

This dilemma has led to the study of alternative detection methods. The PSA test has been fine tuned to detect prostate cancer antigen (PCA), but it still not very specific (only 75% sensitivity). In 2008, a urine test was developed that has a sensitivity of 80% (it can detect 80% of cases) and is 61% effective at ruling out those without the disease. The test looks for the presence of four different RNA molecules associated with prostate cancer. If RNA is present, it is likely that proteins are as well. And some researchers think that the presence of these molecules may give urine a distinctive odor. Because humans have yet to devise an artificial method of separating out the odor molecules, some researchers are testing this theory using dogs.

At the June 2010 meeting of the American Urological Association in San Francisco, two French researchers presented the results from the year they spent training a Belgian Malinois shepherd, a dog breed already used to sniff out drugs and bombs, to sniff out the presence of prostate cancer. At the end of the training, the dog successfully classified 63 out of 66 urine samples. Other researchers are wary of the results – the dog may have picked up on subconscious cues from the investigators.

Many feel that the dogs simply smell what humans cannot. Once that molecule is identified, testing will be simple and won’t require a well-trained dog or unnecessary biopsies.