As dogs live longer lives, cancer becomes main cause of death

Thousands of years ago, people turned wolves into man’s best friend. First, they were seen as pets; now they are considered one of the family. The story of man and dog covers around 30,000 years of co-evolution and is one of the most renowned cases of artificial selection in animal history.

As the story has evolved, so have dogs’ living conditions and an entire industry revolving around their care, including academic disciplines, veterinary specialties and other services. The saying, “It’s a dog’s life” no longer has the same negative connotations. The quality and length of their lives have changed dramatically. With dogs living longer lives, cancer has become the main cause of death.

In the case of large dogs weighing more than 50-60 kilos, the diagnosis of bone cancer occurs on average at the age of five, compared to 11 for dogs under five kilos. Breed also influences the dog’s chances, with purebred dogs diagnosed at the age of 8.2, while the disease does not generally appear in mixed breeds until an average age of 9.2, according to data from a new study published on February 1 in the journal Plos ONE.

Among the breeds that had sufficient representation in the study, researchers were able to determine that mastiffs, Saint Bernards, Great Danes and bulldogs had the youngest mean age for diagnosis, at approximately six, with English mastiffs having the youngest mean age at five. Boxers, Vizslas and Bernese Mountain Dogs had a mean age of 6.1 to seven.

Breeds that tend to show tumors later, at around 10, include dachshunds, cocker spaniels, Australian shepherds, beagles and terriers. At 11 and a half, the bichon frisé has the highest average age of diagnosis. The study also flags up that female and neutered dogs tend to develop cancer later.

Led by geneticist Jill Rafalko, the research focused on a sample of 3,452 US dogs with a cancer diagnosis, taking into account breed, size and gender. From PetDx Pharmaceuticals in La Jolla, California, Rafalko explains that her work aims to “help raise awareness of the importance of early care and popularize preventive screening in dogs,” because it decreases the possibility of damaging cancer treatment in the same way it would with humans.

New prevention model

Rafalko’s pharmaceutical team is promoting the idea of an animal liquid biopsy, a novel method of non-invasive blood analysis that detects tumors before they spread to an organ. The team points out that it would be desirable to “start tests in dogs two years before the average age at which, due to their breed or weight, they might begin to suffer from symptoms of the disease.” This would mean testing some dogs as early as the age of four. Animal oncologist Andi Flory, chief medical officer at the center, explains that developing this cancer detection technique and its animal statistical model is “a way of normalizing prevention.”

Professor Elena Martínez de Merlo, from the Faculty of Veterinary Medicine at Madrid’s Complutense University, explains that “oncology in small animals right now is absolutely up to date, since the incidence of cancer is very high.” She explains that this is due to the importance of these animals in the lives of their owners and to the fact that the field of oncological studies has changed substantially in the last 30 years. According to Martínez, non-invasive preventive therapy is “the future, the path that will be followed,” but she raises doubts as to how “liquid biopsy will measure the seriousness of the cancer, and the types of malignancy.”

“The oncological study in animals always lags behind that of humans, but it changes very quickly,” says Martínez. “Our goals are also different. We are looking for quality of life versus quantity of life.” She considers that the US epidemiological sample cannot be directly extrapolated, but it is consistent with other analyses of cancer in dogs that have been carried out in Europe.

The importance that the welfare of dogs plays in people’s daily lives is something that Noemí del Castillo Magán is also aware of when carrying out treatment at her veterinary clinic Surbatán, in Madrid. “There is a radical generational shift that I see, especially among owners under 40,” she says. “Animal care is a very expensive specialty, so there must be a very big emotional factor.” Both experts flag up the importance of veterinary medicine in ensuring the dog’s quality of life and believe cancer prevention will be the way forward.

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