Tumor Hounds

by Malcolm Riordan

Your dog can be trained - in a matter of weeks - to detect lung, breast, kidney and bladder cancer in human patients.  Fact!

In 1989 The Lancet medical journal published the findings of dermatologists that showed dogs could be trained to recognize malignant melanomas and basal cell carcinomas on the skin of human patients - even through the patient's clothing.  It had all begun when a patient told her doctor that the family dog seemed overly interested, even obsessed with a particular mole on her leg. This somehow had gotten her in to the doctor to have it checked. A malignant melanoma in its earliest stage was diagnosed and removed before it had spread. Both the dog's owner and her dermatologist credit the dog for quite likely saving her life with the early detection.  This turns out to be but an entry level observation in the medical field learning about dogs' ability to detect cancers.

Dogs can detect odors at levels down to one part per trillion – this is on the order of one drop mixed into an Olympic sized swimming pool.  How can we possibly comprehend and conceptualize the complex scent-world of our dogs and what their nose knows?  It is likely that the heightened sense of smell provides our dogs with as much information to process, categorize, respond to, use, remember and learn from as our sense of vision provides us.

Cancer cells release different metabolic waste products than normal healthy cells do. This difference between the metabolic products of a cancerous cell and a healthy cell are great enough that dogs can distinguish between them.  Simple training can teach a dog to alert or signal when they get a whiff of those specific odors from the abnormal waste products of certain types of cancer cells.

The abnormal cells' waste products - molecules of it - get into the blood stream and from there get into the urine and/or the lungs of people with cancer. When these abnormal molecules come out in the urine, or in the exhaled breath from the lungs, dogs are able to detect those molecules from a sample tube of a patient's breath or from a vial of a person's urine. The more easily these molecules diffuse into the air, the more likely that dogs will be able to detect them. This way, if cancer cells of a certain type do release abnormal molecules, and if these molecules will diffuse readily in to the air in the lungs or into the vapor from a urine sample, dogs can be taught to respond with trained behaviors or actions to alert their human handlers when they detect the unique molecules.

Success Rates

Beginning in 2004 studies in the United States and England were done with dogs who were successfully trained to distinguish the exhaled breath of cancer-free human patients from patients' breath who had already been medically diagnosed with either lung cancer or with breast cancer. With lung cancer the dogs were 99% accurate in their simple screening for the presence of lung cancer, and were 94% accurate in detecting the presence of breast cancer, all by smelling breath samples collected in tubes.   Five ordinary household dogs with training over only a few weeks were used in the study.  Essentially, with rare exception, each dog picked out each and every cancer patient, 83 of them, from a group of 166 people.

More recently, a study at a cancer institute in Marin County, California demonstrated that dogs successfully discriminated between samples of exhaled breath from women patients with different types and stages of ovarian carcinoma and breath samples from women without ovarian cancer. These dogs also performed with the astounding success rate of 99%. As with the previous lung cancer/breast cancer study, the dogs identified low grade, early stage cancer patients as readily as they did the patients with more advanced stages of cancer.  We all realize that the earliest detection of cancer can make all the difference in the outcome for a patient.  Interestingly, successful sniffer dogs were from any breed or mix, either gender, and any age.

A study in England showed that in a group of patients - people who had kidney or bladder cancer – and four trained dogs, that the dogs had achieved a successful identification rate of but 42% by sniffing at the human patients' urine samples. Still, that study has achieved legendary status in the medical community, because during the study the four dogs saved a woman's life! 

In tests and diagnostic imaging before the study, urologists had determined that this woman was cancer-free and would be in the study as one of the 'normal' patients.  Yet each of the dogs repeatedly and erroneously alerted on the urine sample of this cancer free woman.  After the study, one of the urologists had a hunch to reassess this 'normal' patient and so put her back through the battery of cancer screening tests and diagnostic imaging. No one else associated with the study had even considered the possibility that the dogs were right.  This retesting of the patient revealed what the dogs had all detected, the urologist now found a tiny spot of cancer in the bladder.  This early detection led to a completely successful intervention. The pre-med rookie dogs were famously correct in their unanimous second opinion!  That patient is alive today owing to canine insistence on what they had smelled, and not being swayed by human assumptions and group-think!!

It looks like not all cancers will be amenable to dogs recognizing them by unique odor. A study with dogs trying to detect prostate cancer in men's urine netted results that were just barely better than random chance would be.  Some tumors just may not emit a biochemical marker for dogs to identify.  And there are probably molecules that just don't tend to evaporate into an odor or vapor, and thus go undetected by dogs.

Dr. Rex Will Smell You Now 

Will we ever hear the words “Dr. Rex will smell you now”?  Disappointingly, no time soon.  So far, only proof of the concept has been established.  More time, more money, more studies are needed, and then there would be the phase of exactly how to implement and integrate dogs into the picture.  If dogs are used in sniffing out cancer, it would only be to screen for these tumors, alerting doctors to begin locating, diagnosing, staging and then treating these cancers.  There will be a lot more early detections than now.

Some in the medical world can envision trained dogs that live as pets at family homes, and then going in to work at the lab, donning a starchy white Doggie Howser lab coat on work days.

Others in the medical field, knowing that cancer is nothing to sniff at, predict that dogs will only be used to collect information on which tumors can be identified by any unique molecular vapors. Meanwhile, highly specialized breathalyzer-like instruments could be developed:   dogs would be replaced with high-tech electronic robo noses.  That is a bit of a long shot gamble, for in the war on cancer, our dogs have clear, unmatched nasal-superiority.