When Cancer in Dogs Isn’t Just Bad Luck

The Golden Effect

Let’s take a look at just one popular breed to see how the genetics of cancer play out. The honey-coated Golden Retriever, who originated in the United Kingdom, was recognized by the AKC in 1925 and ranks third in popularity among AKC registered breeds.

The large number of Golden Retrievers in the United States, plus their devoted families, has resulted in an active research community surrounding this beloved breed. That’s good, because Golden Retrievers are known to have a high risk of hemangiosarcoma, a deadly tumor found in several areas of the body including the spleen, liver and heart. When scientists study the DNA of Goldens diagnosed with hemangiosarcoma and compare it to other breeds of dogs diagnosed with the same disease, the genetic abnormalities are different. Interestingly, American Golden Retrievers differ from their U.K. counterparts: Goldens from the U.K. are largely spared this dreaded disease. When studied in a laboratory, the genes of American and U.K. Goldens are significantly different, suggesting that the risk of hemangiosarcoma is related to a relatively recent genetic alteration.

Lymphoma (cancer of the lymphatic system) is another type of cancer commonly diagnosed in Golden Retrievers. The manifestation of lymphoma and hemangiosarcoma appears to be unrelated except for the frequent occurrence of both in Golden Retrievers. Now, through study of the canine genome, researchers have identified genetic alterations common to Goldens with either lymphoma or hemangiosarcoma. These alterations, or mutations, modify the regulation of the immune system’s surveillance for tumor cells, currently thought to be a common mechanism underlying the occurrence of these two dissimilar tumors in this breed.

Size and Color Play a Role

Though genes are important in the development of certain cancers, a single gene is unlikely to be the sole cause of cancer. For example, the genes controlling size appear to also play a role in the development of canine osteosarcoma, the most common form of bone cancer in dogs. Whippets and Greyhounds are physically very similar, with the Whippet being an apparently smaller version of the Greyhound. The similarity continues at the level of their DNA, and these two breeds are genetically very similar when their genes are compared in a laboratory. However, their risk of developing osteosarcoma, or bone cancer, is very different. This deadly tumor occurs commonly in Greyhounds but is rare in Whippets. In fact, it is uncommon in all dogs weighing less than 25 kilograms, suggesting that the genes controlling body size also play a role in the development of osteosarcoma in dogs.

Genes influencing coat color can also apparently play a role in cancer development. I have cared for a number of black Standard Poodles with multiple toes affected by nail bed (the skin at the base of the toe) squamous cell carcinoma, but never a white, brown or apricot poodle. Recently released data shows a genetic basis for my clinical observation. Standard Poodles diagnosed with nail bed squamous cell carcinoma have a variation in the number of copies of a gene known as KITLG. A similar number of light-coated Standard Poodles also have the same variation in the number of copies of the KITLG, but a simultaneous mutation in a different gene in the lighter-coated poodles apparently protects them from the cancer-promoting effects of the bad gene. Even more interesting is the finding of this same variation in the KITLG gene in Briards and Giant Schnauzers, two other black-coated breeds with an increased risk of developing nail bed squamous cell carcinoma.


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