Cancer In Dogs: Size Does Matter

May 20, 2024

A recent study from UC Riverside, published in the Royal Society Open Science, explored the relationship between size and cancer risk within individual species and breeds. This research supports the multistage model of canine cancer, which suggests that the more cells an animal has, and the longer those cells live, the more opportunities there are for mutations that could lead to cancer.

Interestingly, the findings indicated that this increase in cancer risk with size didn’t apply across different species but was significant within the same species. For instance, it was found that humans showed a 10% increase in cancer risk for every additional 10 centimeters in height, which was a pretty stark contrast to interspecies comparisons where larger animals like elephants exhibited surprisingly low cancer rates despite their massive size and longer lifespans.

Size Matters: Cancer In Dogs May Be Associated With Size Variations

The study’s author, Leonard Nunney, an evolutionary biologist, explained that examining cancer rates in dogs offered a unique perspective because of the vast size variation within the species—from Chihuahuas to Great Danes. This range allowed them to really put the multistage model to the test. The smallest breeds, such as Pomeranians and Shih Tzus, showed around a 10% mortality rate from cancer, whereas medium-sized breeds, including Scottish Terriers and certain types of retrievers, displayed higher than expected rates.
Photo: A Bernese Mountain Dog looks majestically at a mountain side.

Among the larger breeds, Bernese Mountain Dogs stood out, not only for their size but also for their susceptibility to a severe form of cancer known as histiocytic sarcoma. These dogs are beloved for their gentle nature and noble presence in so many families. Sadly, though, they had a mortality rate from cancer exceeding 40%.  Histiocytic sarcoma was found to be particularly devastating and highlighted the critical need for further research and potentially, targeted clinical trials to explore more effective treatments. For instance, while there is research being done to look for treatment options for histiocytic sarcoma in Bernese Mountain Dogs, researchers are having a hard time spreading the word for the need for study participants. (If you know or love a BMD who may be eligible for the study, please find out more here.)

The research also touched upon the phenomenon that larger breeds tended to have shorter lifespans, with every pound increase in breed size shortening life expectancy by about two weeks. This trend actually contributed to lower cancer risk in the very largest breeds like Great Danes, though, as cancer is predominantly a disease of old age–which also supports the multistage model of cancer in that the longer cells live, the more susceptible to cancer in larger breeds they are.

These important findings not only shed light on the patterns of cancer in dogs but also hinted at broader biological processes that could explain how larger animals like whales and elephants had evolved traits to minimize cancer risk despite their long lifespans and large size. It raises fascinating questions about the evolutionary biology of cancer prevention, but more importantly, shows the need for more research about the importance of size as a factor in cancer risk within species. While many breeds simply can’t adjust for their size, and we of course want them to live as long as they can, more research into treatment options as well as prevention strategies could help keep us from losing so many to cancer.

Sign up now to receive the latest updates via email.