The Most Common Cat and Dog Cancers & Their Treatments

If your veterinarian has said your dog or cat could have cancer, don't panic!  Roughly 6 million cats and another 6 million dogs are diagnosed each year. These numbers mean 1:4 dogs and 1:5 cats will be diagnosed with cancer in their lifetime and that researchers are studying the types of cancers in dogs and cats to come up with new ways to keep them on the road to recovery.  Cancer in our pets is actually very common. 

Half of dogs over 10 will develop it at some point, and larger dog breeds have an increased chance of cancer compared to smaller breeds. Cats also have an increased risk of cancer after age 10, with females at increased risk of breast cancer and males for mast cell tumors.  What we’re saying is you’re not alone, and new technology to fight and treat cancers in both dogs and cats are being developed as we speak.

The disease is often predictable and treatable as cancer cells act similarly whether within a person or an animal. One example of a treatment used on humans and pets is chemotherapy and 85% of animals experience no negative side effects. 

Another example can be found in a genetic mutation in the c-KIT gene found in certain Mast Cell tumors of humans, cats, and dogs. Depending on specific location, this mutation is present in up to 30% of dogs, 68% of cats, and 40-80% of human patients. 

In both humans and animals, gene therapies are available that target the c-KIT gene called tyrosine-kinase-inhibitor therapies (TKI’s). One study looked at 42 dogs with this mutation on exon 8 and found 90% survived 2 years post-treatment. Although less studied, cats with mast cell tumors are also responsive to TKIs, with 80% gaining some benefit from treatment. 

If you noticed we’ve mentioned humans and pets in this post.  This is because your veterinarian may compare your pet’s cancer to your body as a way to make it easier to understand.  This is because cancers in dogs and cats are very similar to cancers in us humans. 

In fact, some of our understanding of cancer cell behavior and treatments has been built based on a constant back and forth between studying cancer in ourselves and our pets!  

If your veterinarian has diagnosed your dog or cat with cancer, take a deep breath.  We’re here to help you through the process so you can learn about this disease, what the treatment process will look like, and some of the ways to help you feel confident so your courage can keep your dog or cat strong too.

What Cancer Is

Cancer is the uncontrolled growth of cells, making it a cellular disease, and the word is a collective name for more than 100 diseases. The rapid division and growth of cells that make up the affected tissues are the same in humans and animals. Because there are more than 100 variations of these growths, cancer has different names depending on the type of cell undergoing the uncontrolled growth. 

Think of the body as a garden and the cells as flowers that go through a life cycle of growing, dying, and regrowing. Regular maintenance is usually needed to keep all these flowers (cells) growing strong and prevent the invasion of weeds (cancer). 

Like cancer cells, weeds can pop up seemingly randomly and have the potential to multiply quickly.  When they do they take away space and nutrients from the flowers and plants in the garden if the weeds are not pulled out in their entirety.  

Just like cancer cells, weeds can grow in any part of the garden as they rely on the soil and nutrition your plants need, just like cancer can grow and develop within any living tissue as it uses the same resources and blood supply to thrive. 

Cancer is not a specific organ, lump, or systemic failure, those are just the symptoms caused by the mischief of a cell, or growing group of cells that managed to avoid detection until a concerned pet parent brought their little one into the veterinary office for screening and testing.

Now that you know what cancer is in pets, let's look at how cells become cancerous and then some of the most common types of cancer in both dogs and cats, and how each type is normally treated. 

How Cells Become Cancer

Thankfully, whether it is in cats, dogs, komodo dragons, or humans, cancer cells have the same areas they prefer to grow and share the same range of possible mutations within their DNA. These mutations are referred to as oncogenes, which allow cells to grow, multiply, and avoid death compared to the normal cells around them. 

Cells are like plants and have their own lifecycle which can be broken down into dividing (mitosis) or not dividing (interphase). The DNA in each cell is a script that tells the cells when to grow, when to ship out products to nearby cells, when to divide, and when to undergo programmed cell death (apoptosis). 

In the case of cancer, this script is altered in areas called oncogenes relating to the checks and balances that prevent a cell from dividing uncontrollably.  Eventually, they become cancerous through this continued replication despite the body lacking resources to support those cells.

There are Four Common Cancers in Dogs and Cats

• Bone
• Breast
• Lymphoma
• Skin and Soft Tissue

Bone Cancers

Osteosarcoma is the most common form of bone cancer in children, which develops spontaneously and aggressively.  It is also present in our pets and disproportionately affects larger breeds with an estimated 10,000 cases diagnosed each year. 

A 2023 study found Great Danes, Rottweilers, and the Rhodesian ridgeback all have higher incidences of osteosarcoma compared to other breeds and non-purebred dogs. This is the most common form of bone cancer in cats, accounting for 70-80% of bone cancers, and unlike in dogs and humans, it is rare and less aggressive.

While children are often treated conservatively to preserve their limbs, the first line of treatment in dogs with osteosarcomas is amputation of the affected limb combined with chemotherapy. After treatment, 45-50% of dogs gain another year of life with their families, and 20% are still running around after 2 years. 

Cats have lower recorded incidences of metastasis, and treatment involves only surgery, either limb-sparing or amputation. To improve the outcomes of cats and dogs affected by osteosarcomas, research centers like Cornell University are attempting to make a vaccine.

Breast Cancer 

Another common type of cancer in dogs and cats is breast cancer, disproportionately affecting both human women and female dogs and cats.  Breast cancer is the second most common cancer in dogs and the 3rd most common tumor in female cats, which 80% of the time is malignant and aggressive. 

In cats and dogs, the risk of breast cancer increases depending on if they are spayed before or after 12 months of age, with being spayed after 12 months increasing their risk levels.  Just like in humans, this cancer is often detected by palpation of the breast tissue/nipple area and possible leakage from the nipple, imaging, and taking a biopsy or fine-needle-aspirate (FNA) of the affected area for testing. 

Treatment for feline and canine breast cancer usually includes removal of the mass and a spay (if your pet has not been spayed already), with chemotherapy introduced if the cancer has spread. 

For dogs, 50% of mammary tumors are benign and cured by surgery. For cats, the size of the tumor and the aggressiveness of the surgery heavily affect the prognosis. If the tumor is larger than 3cm (about the size of a grape), the life expectancy is 4-12 months for affected cats after treatment. Cats whose tumors were detected early (smaller than a grape) have a better survival rate post-treatment at 21-24 months. 

Lymphoma

Lymphoma affects 30:100,000 dogs, making it the most common hematopoietic tumor, which is a kind of cancer that involves the cells of the immune system: the white blood cells. Just like humans, where lymphoma can be caused by viruses like EBV and HIV, lymphoma in dogs and cats can be caused by viruses, their environment, or even be predisposed due to genetics. 

Lymphomas occur largely in middle-aged dogs, with some studies pointing to a genetic predisposition in Bullmastiffs, and other retrospective studies favoring Maltese, Shih-tzu, Cocker spaniels, Scottish terriers, Boxers, beagles, or German shepherds. 

According to one study, Centroblastic Lymphoma (CBL) is most commonly found in Rottweilers, Bernese mountain Dggs, and golden retrievers. Highly individualized immunotherapy and chemotherapy are often on the treatment plans for animals affected by lymphomas. 

Skin and Soft tissue Cancer

Just like humans, sun exposure can lead to cancer, such as the case of a 10-year-old white-coated cat developing fibrosarcoma (a type of soft tissue cancer) of its ears due to UV radiation. 

Melanoma, which accounts for 70% of melanocytic tumors and 7% of cancer diagnoses overall in dogs, is usually identified in the mouth or under the tongue of highly pigmented breeds, with Scottish terriers, golden retrievers, poodles, dachshunds, and chow-chows at higher risk compared to other breeds. 

In cats, melanocytic tumors account for less than 1% of cancer diagnoses, with 67% occurring in the eyes and tumors in the mouth being rare. In Humans, melanomas account for 1% of cancer diagnoses but have the highest mortality rate of skin cancer. 

A vaccine called Oncep for melanoma in dogs using human proteins has actually been developed to help treat this cancer beyond surgical removal and chemotherapy. However, it requires further study to prove its effectiveness. 

How Cancer is Treated

Because cancer is a cellular disease, and what we see and our pets experience are the symptoms, treatment begins at the cellular level, often involving surgical removal of the cancerous tissue and chemotherapy/radiation to target any remaining stragglers.

Some types of cancer can be targeted via cellular therapies like immunotherapy, one version of which is a vaccine and uses the body’s own immune system to locate the cancer cells via the abnormal proteins they give off and kill them by causing the body to no longer recognize those cells as ‘self.’

This type of therapy allows for more specific targeting of cancer cells via one’s own immune system, as chemotherapy and radiation have the possibility of hitting both cancerous and normal tissue. 

The lethargy, loss of playfulness, and general unexpected change in the behavior of our cats and dogs could be a sign that they no longer have the extra energy to support their quirks.  The food they eat is now supplying energy to the cancer cells vs their body and the cancer cells are using it while they are constantly dividing. 

Per the American Veterinary Medical Association, some other symptoms include non-healing wounds, sudden weight gain/loss, visible growths or skin changes, and difficulty with basic functions like eating and breathing. 

Cancer diagnosis and treatment decisions are made differently for each individual dog or cat and by their medical caregiver. The type of cancer and symptoms your pet displays affect how they are treated, although some breeds may be more susceptible to certain types of cancer compared to others. 

Unfortunately, cancer treatments have their own side effects, including nausea, vomiting, secondary infections, and diarrhea, depending on the area being treated.  And some could last for up to six months after completion of treatment. 

With that said there are steps we can take to help support our pets holistically and alleviate some of these symptoms, such as acupuncture, probiotics, and even CBD for cellular support with vet consultation.  Yes, cancer is a scary word for all pet parents to hear, but new treatments and technologies are becoming available all the time.  Keep your spirits high and stay strong, you’re not alone and there is always hope.