Princeton's Ask the Doctor May/June 2019

Can Dogs Sniff Out Cancer? By Pam Teel

Dogs have an excellent sense of smell, so much better than our human noses. Dogs have 25 times more smell receptors than humans, boosting their smelling ability by 100,000 times. It is a true fact that that a dog’s olfactory abilities are so great that he can potentially sniff out cancer in humans. The brain of a human is dominated by the visual cortex, but the brain of a dog is controlled by the smell or olfactory cortex, which is approximately 40 times larger than that of a human. The olfac- tory bulb in a dog has a large number of smell-sensitive receptors, which range between 125 to 300 million, and it is a hundred thousand to a million times more reactive than that of humans. In addition, dogs have a second smelling device in the backs of their noses that we don't have, called Jacobson's organ. That double smelling system allows trained dogs to detect cancer's unique odors, called volatile organic compounds. Studies of dogs and cancer detection are based on the fact that cancerous cells release different metabolic waste products than healthy cells in the human body. The difference of smell is so significant that the dogs are able to detect it even in the early stages of cancer. Dogs are able to identify the chemical traces in the range of parts per trillion. Some studies have confirmed the ability of trained dogs to detect the skin cancer melanoma by just sniffing the skin lesions. Furthermore, some researchers have proven that dogs can detect prostate cancer by simply smelling patients’ urine. Dogs may also be able to sniff out the presence of cancerous cells through a human’s breath. The ability of dogs to detect cancer has great potential benefits. Some researchers believe the trained dogs will become integrated di- rectly into patient care, while other researchers recommend the skills of the cancer-detecting dogs be confined to the laboratories, where the gas chromatographs could be used to isolate the specific compounds that are identified by the dogs. Recent developments in this area include a simple breathalyzer that can change color according to the compounds in the breath indicating the presence of cancer. In a research study conducted by the Pine Street Foundation, breath samples of 31 breast cancer patients, 55 lung cancer patients and 83 healthy people were presented to five trained scent dogs (three Labrador retrievers and two Portuguese water dogs). These dogs were able to detect or rule out breast and lung cancer, at all stages of the disease, with approximately 90 percent accuracy. An expert in melanomas, Dr. Armand Cognetta of Tallahassee, studied whether dogs could detect skin cancer and enlisted the help of a dog trainer. With the samples of melanomas, he worked to train a dog to sniff out the skin cancer. The dog used in the study was able to detect the melanoma approximately 99 percent of the time. Furthermore, this research proved that the dog could successfully detect the malignant melanoma lesions from the benign lesions in patients. Millstone Township resident Linda C. will tell you that her Brittany Spaniel, Holly, found her cancer and literally saved her life. Linda has stage 4 Invasive Ductal Carcinoma that spread to her liver and spine. She had a lumpectomy and then heavy chemo, which put her in remission in 2014, but it was her dog that she believes initially found her cancer. The dog literally tried to dig it out of her chest. As she gave out a high pitch cry, the dog kept digging, to no avail. This strange behavior prompted Linda to go to the doctors. They found the cancer when it was 2mm. If Linda hadn’t listened to the dog and thought something was not right, she would never have gone to the doctors because she didn’t feel it and she wasn’t sick. She fully credits Holly for saving her life. “She found my cancer again this time. She would snuggle and sniff my breast and lay on top of me hugging me. She’s an awesome girl and we feel blessed to have her,” Linda stated. In the United Kingdom, Lucy, a cross between a Labrador retriever and an Irish Water Spaniel, failed miserably at guide dog school. Bred to be a hunting dog, she had a good nose. For the next seven years, Lucy learned to sniff out bladder, kidney and prostate cancer, and was even used in a study. Over the years, she has been able to detect cancer correctly more than 95% of the time. That's better than some lab tests used to diagnose cancer. Now, Lucy is part of one of the largest clinical trials of canine cancer detection. A British organi- zation, Medical Detection Dogs, has eight dogs sniff out 3,000 urine samples from National Health Service patients to see whether they can discern who has cancer and who doesn't. Claire Guest is the CEO of Medical Detection Dogs. Her Fox Red Labrador, Daisy, much like Linda’s dog Holly, caught her breast cancer six years ago when she was 45. "She kept staring at me and lunging into my chest. It led me to find a lump," Guest remembers. The tumor was deep in her breast. Her doctors said that by the time she would have felt it herself, the cancer would have been very advanced. "Had it not been drawn to my attention by Daisy, I'm told my prognosis would have been very poor," she said. In 1989, doctors at King's College Hospital in London wrote in The Lancet about a woman whose dog persisted in smelling a particular mole on her leg. That mole turned out to be early-stage malignant melanoma. Over the next 26 years, studies from France to California to Italy have concluded that dogs really can detect the smell of cancer. Using dogs to find cancer in a therapeutic setting would need a lot of years of study and a lot of development. It's still far from that and it probably wouldn't be a realistic way to screen patients. It would take an immense amount of resources to train dogs to recognize the many types of cancer that can affect humans. In addition, while no test is perfect, at least doctors know how accurate different tests, such as mammograms, are and at what rate they produce false positives and false negatives. But these rates would vary for each dog. Moreover, dogs can get bored, hungry and have bad days. You'd have to be carefully monitoring their effectiveness throughout their cycles. Both Linda and Clair were very lucky that an unlikely hero came along in their lives at a time when they needed them most.

H E A L T H A R T I C L E S A N D Q & A

12

ASK THE DOCTOR

MAY/JUNE 2019