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Large-Scale Cancer Study of Golden Retrievers Holds Hope For All Dogs
On the trail of canine cancer
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In Dog Diseases Treated by Homeopathy (first published in 1863, before chemotherapy, radiation, biopsies and blood panels), author James Moore advised concerned dog owners on treating cancer: “An operation cannot remove the cancer, but it can remove the tumor, which causes much suffering; the knife is, therefore, merely palliative in its effect. Still, the disease, even then, is likely to return at a period more or less remote.”

Today, the diagnosis isn’t as bleak. Indeed, 50 percent of all canine cancers are curable if caught early enough. Moreover, the disease is mostly an aff liction of old age (tragically, some cancers strike dogs as young as two). It may seem like more dogs get cancer than ever before, but it’s presumably because they enjoy a longer life span, thanks to vaccinations against infectious diseases like parvovirus and distemper, and new treatments for congenital, degenerative and metabolic disorders.

“Cancer” is the broad term for a complex cluster of more than a hundred diseases. Although there are many causes, each type of cancer starts with alterations in genes that tell cells how to function, which triggers accelerated and uncontrolled cell growth. The defective signal may hide in abnormal genes inherited from parents, or germinate when normal genes are exposed to harmful environmental influences.

Some breeds are predisposed to certain types of cancer, and in those cases, a strong inherited genetic component is suspected. It is thought that a small number of genes account for cancer risk, but, although they are directly related to the development of individual cancers, rarely is a single gene the sole cause.

By the time people and dogs pass 70 and 10 years of age, respectively, about 50 percent will have been diagnosed with some type of cancer. The malady accounts for approximately 23 percent of all deaths in people. In dogs, cancer mortality varies across breeds, from under 10 percent to higher than 60 percent.

In general, small dogs weighing less than 20 pounds are at very low risk. (Small dogs have lower levels of IGF-1, a hormone that is related to bone and tissue growth. Researchers suspect this may be one reason they have a lower incidence of cancer.) For instance, the chance that a Chihuahua, Dachshund, Maltese, Miniature Pinscher or Pomeranian will get cancer is less than 10 percent. Breeds with the highest risk include the Bernese Mountain Dog, Bouvier des Flandres, Boxer, Bullmastiff and Golden Retriever (Fleming et al. 2011).

Goldens as Case Studies
The high incidence of cancer in Golden Retrievers appears to be a relatively recent phenomenon. Although the breed was neither over- nor under-represented in a 1988 health study conducted by the University of Pennsylvania School of Veterinary Medicine (Prymak et al. 1988), a health report published 10 years later by the Golden Retriever Club of America (GRCA) identified cancer as the cause of death in 61.4 percent of their dogs (Glickman et al. 1999).

Interestingly, cancer risk in Europeanbred Goldens appears to be significantly lower. A 2010 study put the mortality figure at 38.8 percent (Dobson 2012, Adams et al. 2010). Although much higher than average, the incidence is substantially lower than that found in North American Goldens.

Goldens in Europe and the U.S. may look similar, but there are enough DNA differences to separate the dogs into two distinct populations corresponding to their geographic regions. Gene pools on both continents are large, so breeding between the two populations is rare.

When studied in the lab, genomic differences  suggest that risk for some types of cancer is related to recent genetic mutations in North American Golden Retrievers. And this could be good news: genetic differences between European and North American Golden Retrievers may be key to understanding the etiology of canine cancer overall.

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Jane Brackman, PhD, is an authority on the cultural history of canine domestication and the author of two books on pets in 19th-century America. See her new pup, Barkley, and watch him grow on her blog.

doctorbarkman.blogspot.com

Photo of Sandy by Phil Samuell
Photo of Zoe by Andrea Basista

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