Dogs' average age at cancer diagnosis is associated with size, sex, breed

A new analysis has determined median ages of cancer diagnosis for dogs with different characteristics, providing support for the establishment of cancer screening guidelines that vary according to breed or weight. Jill Rafalko of PetDx in La Jolla, California, and colleagues present these findings in the open-access journal PLOS ONE.

More adult dogs die from cancer than from any other cause. Just as in humans, detecting canine cancer earlier can enable more effective treatment. New, noninvasive blood tests for dogs can detect tumor DNA long before other signs of cancer arise. However, formal guidelines for when dogs should be screened using these tests are lacking.

To aid establishment of such guidelines, Rafalko and colleagues sought to determine the median age at cancer diagnosis of dogs with different characteristics. Their analysis included 3,452 dogs with cancer in the U.S.

They found that the median age at cancer diagnosis for dogs weighing 75 kilograms or more was 5 years, compared to 11 years for dogs weighing 2.5 to 5 kilograms. The mean diagnosis age for purebred dogs was 8.2 years, compared to 9.2 years for dogs whose breed was described as mixed or "other."

Among breeds with enough representation in the study, the researchers were able to determine that Mastiffs, Saint Bernards, Great Danes, and Bulldogs had the youngest median diagnosis age, at approximately 6 years. Irish Wolfhounds, Vizslas, and Bernese Mountain Dogs had median diagnosis ages of 6.1 to 7 years. At 11.5 years, the Bichon Frise had the oldest median diagnosis age.

Female dogs were typically diagnosed at older ages than males, and dogs that were neutered were diagnosed later than intact dogs.

The researchers also developed a statistical model to predict median diagnosis age based on weight, which could be applied to breeds with less representation in the study and to mixed-breed dogs.

Considering these findings in combination with evidence from prior studies, the researchers propose that canine cancer detection could be improved through blood test-based screening beginning 2 years before a dog reaches the median diagnosis age for their breed or weight.

The authors add, "Dogs now have a new option for cancer screening called 'liquid biopsy' which, similar to the human version of this test, leverages next-generation sequencing technology to detect multiple types of cancer using a simple blood draw. However, the age to start screening for cancer in dogs can vary depending on their breed or weight. Our study, involving over 3,000 cancer-diagnosed dogs, found that all dogs should begin cancer screening at age 7, but certain breeds may benefit from screening starting as early as age 4."