Brain cancer in dogs results primarily from genetic factors tied to breed, with age playing a significant secondary role. Most brain tumors appear in dogs older than 5, with certain breeds facing dramatically higher risk due to inherited genetic variants. Unlike many cancers in humans, no specific environmental toxin or lifestyle factor has been clearly linked to brain tumor development in dogs.
The Two Main Types of Brain Tumors
The most common primary brain tumor in dogs is meningioma, which grows from the membranes lining the brain rather than the brain tissue itself. These tumors compress or invade the brain as they grow. The second most common type is glioma, which develops from the supportive cells within the brain. A less common third type, choroid plexus tumors, grows from the tissue that produces spinal fluid.
Each type tends to appear at different ages. The median age at diagnosis for gliomas is 8 years, for meningiomas 10.5 years, and for choroid plexus tumors 5.5 years. The vast majority of brain tumors are diagnosed in dogs over 5 years old.
Breed and Genetics Are the Strongest Risk Factors
Genetics plays a larger role in canine brain cancer than in almost any other factor researchers have studied. The link is so strong that certain breeds face risks many times higher than the general dog population. Boxers have a relative risk of glioma roughly 23 times higher than average. Bulldogs and Boston Terriers face about 5 times the normal risk.
The pattern follows skull shape in a striking way. Flat-faced (brachycephalic) breeds are far more prone to gliomas, while long-nosed (dolichocephalic) breeds like Golden Retrievers are more likely to develop meningiomas. Golden Retrievers, Miniature Schnauzers, and Rat Terriers are all overrepresented among meningioma cases. Gliomas cluster heavily in Boxers, Boston Terriers, Bullmastiffs, and English and French Bulldogs.
Researchers have traced part of this risk to a specific region of the genome. A genetic study published in PLOS Genetics found that the DNA region associated with glioma risk in brachycephalic breeds overlaps with a region linked to the flat-faced skull shape itself. This suggests that when breeders selected for shorter snouts over generations, they may have inadvertently concentrated cancer-promoting gene variants in those same bloodlines. The glioma risk likely hitchhiked along with the genes for a desirable physical trait.
Even among flat-faced breeds, the biology isn’t identical. RNA sequencing of brain tumor tissue found 31 genes expressed differently in French Bulldogs compared to Boxers and Boston Terriers, with differences in cell growth regulation, cancer-promoting pathways, and immune function. This means the genetic route to the same type of tumor can vary from breed to breed.
There is also a worrying pattern of brain tumors appearing in younger dogs of certain breeds, particularly Boxers and Boston Terriers, suggesting their genetic predisposition can override the usual age-related timeline.
Cancer Spreading From Elsewhere in the Body
Not all brain cancer starts in the brain. Tumors that originate in other organs can metastasize to the brain, and this accounts for a meaningful share of canine brain cancer cases. A study of 58 dogs with brain metastases found clear patterns in where these secondary tumors came from.
Hemangiosarcoma, a cancer of blood vessel walls, was the source in over half of all cases (53%). Carcinomas (cancers of organ lining tissues) accounted for about 28%, and melanoma (a skin cancer) made up 12%. The remaining cases involved other types of soft tissue cancers. If your dog has been diagnosed with one of these cancers elsewhere in the body, there is a real possibility of it eventually reaching the brain.
What About Infections and Inflammation?
Some dog owners wonder whether infections or chronic brain inflammation could trigger tumor growth. Researchers have investigated this question, particularly in the context of necrotizing meningoencephalitis, a serious inflammatory brain disease. Despite extensive molecular testing, no consistent infectious agent has been identified as a contributor. Viral infections can produce brain lesions that look very similar to inflammatory disease on a microscope slide, but rigorous testing has not confirmed a virus as a cause of brain tumors.
The short answer is that no infection, vaccine, diet, household chemical, or environmental exposure has been reliably demonstrated to cause brain cancer in dogs. This doesn’t mean environmental factors play zero role, but it does mean that genetics and age remain the only well-supported risk factors in current veterinary science.
Why Age Matters
Like most cancers, brain tumors become more likely as a dog gets older. The cells in a dog’s body accumulate DNA damage over a lifetime, and the brain’s own repair mechanisms become less effective with age. Most primary brain tumors are diagnosed in middle-aged to senior dogs. If your dog is a predisposed breed and entering its senior years, any new neurological symptoms (seizures, behavior changes, difficulty walking, head tilting) warrant prompt veterinary evaluation, ideally with an MRI. Veterinary neurologists particularly recommend imaging for breeds like Boston Terriers when signs point to problems in the brainstem or cerebellum, given their elevated glioma risk.